[SDL Utility] Add beige color for the map default background.
[SDL Widget] Reorder state assignment (from on to off) so that the callback may change the button state (i.e. to disable or hide it).
[SDL Manager] Implement layers: background, non-interactive, and interactive layers.
[Game Manager] Utilizer SDL Manager's layers. Change how the buttons are created (not use sdl.createButton()).
[makefile] Stop hardcoding all the builders, and use a variable instead. Add pedantic flag.
[main] Fix alignment.
[main] Utilize SDL Manager's layers.
[SDL Map View] Implement a Map View widget. It's light yellow.