Provide more control over the SDL window

[aschaeffer]

• Make the SDL window states available in the screen_manager
• Process SDL_WindowEvents (https://wiki.libsdl.org/SDL_WindowEvent) and update the screen_manager states
• Make the screen_manager available in the Inexor Tree
  • Allows Inexor Flex and user interfaces to manipulate the window states

Inexor Tree Path	SDL_EVENT	Description
/rendering/window/x	SDL_WINDOWEVENT_MOVED	The window position (x)
/rendering/window/y	SDL_WINDOWEVENT_MOVED	The window position (y)
/rendering/window/width	SDL_WINDOWEVENT_RESIZED SDL_WINDOWEVENT_SIZE_CHANGED	The window size (width)
/rendering/window/height	SDL_WINDOWEVENT_RESIZED SDL_WINDOWEVENT_SIZE_CHANGED	The window size (height)
/rendering/window/shown	SDL_WINDOWEVENT_SHOWN SDL_WINDOWEVENT_HIDDEN SDL_WINDOWEVENT_EXPOSED	Window shown or hidden
/rendering/window/minimized	SDL_WINDOWEVENT_MINIMIZED SDL_WINDOWEVENT_MAXIMIZED SDL_WINDOWEVENT_RESTORED	Window minimized / maximized / restored
/rendering/window/mouse/entered	SDL_WINDOWEVENT_ENTER SDL_WINDOWEVENT_LEAVE	If the mouse has entered the window
/rendering/window/keyboard/focus	SDL_WINDOWEVENT_FOCUS_GAINED SDL_WINDOWEVENT_FOCUS_LOST SDL_WINDOWEVENT_TAKE_FOCUS	Window has focus (keyboard input)
/rendering/window/closed	SDL_WINDOWEVENT_CLOSE	Window closed