Loading screen overhaul POC

The loading screen has been significantly changed:
- The background image is now properly picked randomly instead of taking the `textures/logo.bmp` file, prepended by an external program such as Rainsted/Starter.
- The progress bar has been moved from a floating window to a thin green line at the bottom of the loading screen.
- The log window is now hidden by default. It can be turned on by setting `loadinglog` to `true` in `eu07.ini`.
- There is an animated wheel icon on the loading screen, and a trivia text is displayed.

New translation key:
- `"Did you know"`

TODO:
- Load trivia from a separate file.

launcher/launchermode.h

@@ -18,17 +18,13 @@ public:
 	launcher_mode();
 // methods
 	// initializes internal data structures of the mode. returns: true on success, false otherwise
-	bool
-	    init() override;
+	bool init() override;
 	// mode-specific update of simulation data. returns: false on error, true otherwise
-	bool
-	    update() override;
+	bool update() override;
 	// maintenance method, called when the mode is activated
-	void
-	    enter() override;
+	void enter() override;
 	// maintenance method, called when the mode is deactivated
-	void
-	    exit() override;
+	void exit() override;
 	// input handlers
 	void on_key( int Key, int Scancode, int Action, int Mods ) override;
 	void on_cursor_pos( double const Horizontal, double const Vertical ) override { ; }