Improved blit performance

-Disabled alpha where not needed
-Changed graphics to 8-bit color
-Changed the color key on sprites.png
-Used caching for the blockgrid
Merge branch 'master' of https://github.com/CorundumGames/Invasodado
Added in a general MenuState class

-MainMenu, HighScoreState, and SettingsMenu now derive from it
-Removed difficulty settings (I don't feel they add value)
-Moved config.toggle_color_blind to settings.py
-Resolved merge conflicts in color.py
Simplified code that turns enemies and blocks white on pause

-BallOfLights now turn white, too
-Adapted Enemys and UFOs to this
-Added the updated settings-en.wtf file
Made small changes

-Cleaned up and added some documentation
-Fixed a potential bug in loading default scores