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/launcheruilayer.h

@@ -23,6 +23,8 @@ public:
 
 private:
 	void render_() override;
+	void close_panels();
+	void open_panel(ui_panel *panel);
 
 	ui::vehicles_bank m_vehicles_bank;
 	scenery_scanner m_scenery_scanner;