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/editorTerrainStreamer.hpp

@@ -132,6 +132,10 @@ class terrain_streamer
 	void water_material(std::string const &Material);
 	// modifiers: added or replaced by name
 	void modifier(heightmap::modifier Modifier);
+	// many at once, as the formation of all the tracks: each chunk they reach is led anew once
+	void modifiers(std::vector<heightmap::modifier> Modifiers);
+	// the modifiers whose names start so are forgotten, the chunks keep their heights till they're made anew; returns how many
+	std::size_t drop_modifiers(std::string const &Prefix);
 	bool remove_modifier(std::string const &Name);
 	// the ground takes the shape the modifier gives it for good, and the modifier is removed: from then on the
 	// terrain there is shaped by hand like anywhere else
@@ -249,7 +253,10 @@ class terrain_streamer
 	std::vector<editor_terrain *> chunks_in(glm::dvec2 const &Min, glm::dvec2 const &Max, bool const Load);
 	// leads the heights of the chunk from its base heights through the modifiers, within the rectangle
 	void apply_modifiers(editor_terrain &Chunk, glm::dvec2 const &Min, glm::dvec2 const &Max);
+	// the same with the rectangles the modifiers reach, as modifier_bounds() gives them, worked out once for many chunks
+	void apply_modifiers(editor_terrain &Chunk, glm::dvec2 const &Min, glm::dvec2 const &Max, std::vector<std::pair<glm::dvec2, glm::dvec2>> const &Bounds);
 	void apply_modifiers(glm::dvec2 const &Min, glm::dvec2 const &Max);
+	std::vector<std::pair<glm::dvec2, glm::dvec2>> modifier_bounds() const;
 	void build_water();
 	void clear_water(bool const Touch);
 	std::string pack_path(heightmap::pack_key const &Key) const;