Camera follows player

Set up an OrthographicCamera that has Avatar in center of screen at all
times. Default initial Avatar position has been moved. Button font may
now be tinted (red font for world scene action button now, and default
button color is now just tinted from white). Use SpriteCache for drawing
the static parts of map tiles (i.e. parts that do not animate) for
efficiency purposes. Renamed Celdroids Client Desktop/lib folder to
Celdroids Client Desktop/libs for consistency with other projects. More
extensive use of named constants rather than magic numbers in world
scene code.