Launcher improvements

Launcher windows are more Starter-like now:
- The scenery picker, vehicle list and keymapper buttons are now tied to the top portion of the screen.
- The current window is spanning the entire rest of the screen.
- Scenarios are now grouped into categories in the exact same way as Starter does.
- Some drawbacks include:
  - Currently you cannot edit the current trainset, as the vehicle picker window overwrites the scenario list window.
  - The GUI doesn't update when the screen resolution is changed.

launcher/scenery_list.cpp

@@ -5,6 +5,8 @@
 #include "renderer.h"
 #include "application.h"
 #include "Logs.h"
+#include "translation.h"
+
 #include <filesystem>
 
 ui::scenerylist_panel::scenerylist_panel(scenery_scanner &scanner)
@@ -12,6 +14,21 @@ ui::scenerylist_panel::scenerylist_panel(scenery_scanner &scanner)
 {
 }
 
+bool ui::scenerylist_panel::on_key(int key, int action)
+{
+	if (!is_open)
+		return false;
+
+	auto it = keyboard.keytonamemap.find(key);
+	if (it == keyboard.keytonamemap.end())
+		return false;
+
+	if (Global.ctrlState && it->second == "delete")
+		purge_selected_trainset();
+
+	return true;
+}
+
 void ui::scenerylist_panel::draw_scenery_list()
 {
 	// Draw all the scenarios which are not assigned to any category.
@@ -355,6 +372,11 @@ void ui::scenerylist_panel::draw_droptarget(trainset_desc &trainset, int positio
 	}
 }
 
+void ui::scenerylist_panel::purge_selected_trainset()
+{
+	selected_trainset->vehicles.clear();
+}
+
 ui::dynamic_edit_popup::dynamic_edit_popup(ui_panel &panel, dynamic_desc &dynamic)
     : popup(panel), dynamic(dynamic)
 {