feat(editor): labels for a layman, light at the start; whole sceneries fitted to the terrain model

Labels:
- every button, field, tooltip and message of the editor reread for a beginner: short nouns for the fields with the
  sentence in the tooltip, the less used options under More settings, one glossary (field of work, template, track,
  grade), sides told from directions, degrees and per mille as signs, messages built from one format string
- plural forms through STR_P; the last entry of a po file is read too, and the Polish plural rule is in the header
- lang/editor_pl.po: the code pass entries merged, 391 entries no code uses and 3 duplicates dropped
- roads: the notes and errors naming a road translated; the build options and the layout fold the texture length,
  kerb sizes, traffic share, roundabout part, height over the ground and junction speed limit under More settings, the
  lanes start folded

Grade lines fitted to the terrain model (NMT), a line or the whole scenery at once:
- fit_ground: a robust fit on nodes 5 m apart; the ground parting from the line (a bridge, a viaduct, a wall) is gone
  past rather than followed, the bends keep off the switches as far as their curves reach, a run of bends the same way
  is one point of intersection, a curve with no room is as sharp as the room lets it be
- the ends of the line and the other paths of its switches leading into lines fitted already bound the line by what
  the tracks between can climb; ends meeting in the plan, laid apart in height by hand, are joined before the run
- apply_profile: the paths are split where split_path takes the parameter (a straight was cut in the wrong place, into
  pieces of a few centimetres the game takes for zero length), no piece shorter than the margin; the paths off the
  ends of the route are brought to its height
- Bytom: 1600 lines, grade breaks at the joints 89 -> 20; Tarnowskie Gory: 848 lines, 223 -> 3; no step over 2 cm

editor/editorIncludeInfo.cpp

@@ -12,6 +12,8 @@ http://mozilla.org/MPL/2.0/.
 
 #include "utilities/Globals.h"
 #include "utilities/utilities.h"
+#include "utilities/translation.h"
+#include "editor/editorFormat.hpp"
 
 #include <yaml-cpp/yaml.h>
 
@@ -96,7 +98,7 @@ bool read_template(std::string const &File, template_text &Text, std::string &Er
 	std::ifstream input{Global.asCurrentSceneryPath + File, std::ios_base::binary};
 	if (false == input.is_open())
 	{
-		Error = "can't open file \"" + File + "\"";
+		Error = format(STR_C("can't open file \"%s\""), File.c_str());
 		return false;
 	}
 	auto &content{Text.content};
@@ -248,7 +250,7 @@ bool parse(template_text const &Text, include_info &Info, std::string &Error)
 		}
 		if (false == document.IsMap())
 		{
-			Error = "the description isn't a list of named values";
+			Error = STR_C("the description isn't a list of named values");
 			return false;
 		}
 		Info.name = document["name"].as<std::string>("");
@@ -293,7 +295,7 @@ bool parse(template_text const &Text, include_info &Info, std::string &Error)
 	}
 	catch (YAML::Exception const &exception)
 	{
-		Error = std::string{"the description is malformed: "} + exception.what();
+		Error = format(STR_C("the description is malformed: %s"), exception.what());
 		return false;
 	}
 	return true;
@@ -355,7 +357,7 @@ bool save(std::string const &File, include_info const &Info, std::string &Error)
 		auto document{YAML::Load(text.yaml)};
 		if (false == document.IsNull() && false == document.IsMap())
 		{
-			Error = "the existing description isn't a list of named values";
+			Error = STR_C("the existing description isn't a list of named values");
 			return false;
 		}
 		if (false == document["version"].IsDefined())
@@ -427,7 +429,7 @@ bool save(std::string const &File, include_info const &Info, std::string &Error)
 	}
 	catch (YAML::Exception const &exception)
 	{
-		Error = std::string{"the existing description is malformed, fix or remove it first: "} + exception.what();
+		Error = format(STR_C("the existing description is malformed, fix or remove it first: %s"), exception.what());
 		return false;
 	}
 	if (false == text.utf8)
@@ -458,7 +460,7 @@ bool save(std::string const &File, include_info const &Info, std::string &Error)
 	if (output.fail())
 	{
 		std::filesystem::remove(filepath + ".tmp", error);
-		Error = "can't write file \"" + File + "\"";
+		Error = format(STR_C("can't write file \"%s\""), File.c_str());
 		return false;
 	}
 	// the first save of a file leaves its original content next to it
@@ -469,7 +471,7 @@ bool save(std::string const &File, include_info const &Info, std::string &Error)
 	std::filesystem::rename(filepath + ".tmp", filepath, error);
 	if (error)
 	{
-		Error = "can't replace file \"" + File + "\": " + error.message();
+		Error = format(STR_C("can't replace file \"%s\": %s"), File.c_str(), error.message().c_str());
 		std::filesystem::remove(filepath + ".tmp", error);
 		return false;
 	}
@@ -555,14 +557,14 @@ bool complete(include_info const &Info, int const Parameters, std::string *Issue
 	std::string issue;
 	if (Info.name.empty())
 	{
-		issue = "the template needs a name";
+		issue = STR_C("the template needs a name");
 	}
 	for (auto id = 1; id <= Parameters && issue.empty(); ++id)
 	{
 		auto const lookup{std::find_if(std::begin(Info.parameters), std::end(Info.parameters), [=](include_parameter const &Parameter) { return Parameter.id == id; })};
 		if (lookup == std::end(Info.parameters) || (false == automatic(lookup->role) && lookup->value.empty()))
 		{
-			issue = "(p" + std::to_string(id) + ") needs a default value, or a role filled in by the editor (name, pos.*, rot.*)";
+			issue = format(STR_C("(p%d) needs a default value, or a role filled in by the editor (name, pos.*, rot.*)"), id);
 		}
 	}
 	if (false == issue.empty() && Issue != nullptr)
@@ -763,7 +765,7 @@ include_entry examine(std::string const &File)
 	entry.described = false == text.yaml.empty();
 	if (false == entry.described)
 	{
-		entry.issue = "the template has no description";
+		entry.issue = STR_C("the template has no description");
 		return entry;
 	}
 	include_info info;
@@ -791,8 +793,9 @@ void editorIncludeBank::scan()
 	m_scanned = true;
 	std::error_code error;
 	auto const root{std::filesystem::path(Global.asCurrentSceneryPath)};
-	// NOTE: on an error the iterator turns into the end one
-	for (std::filesystem::recursive_directory_iterator file{root, std::filesystem::directory_options::skip_permission_denied, error}, end; file != end; file.increment(error))
+	// NOTE: on an error the iterator turns into the end one. Folders linked into the scenery folder are a part of it
+	auto const options{std::filesystem::directory_options::skip_permission_denied | std::filesystem::directory_options::follow_directory_symlink};
+	for (std::filesystem::recursive_directory_iterator file{root, options, error}, end; file != end; file.increment(error))
 	{
 		if (false == file->is_regular_file(error))
 		{