mega patch:
  new class: platakart sprite
  new modules: sprite, kart
  refactored kart into individual platakart sprites
  removed unused deaccelerate method from kart
  created kart factory (mostly complete)
  removed default values from the kart class (before patch was a mix of default values and values pulled from karts.ini)
  kart factory will load all known values from karts.ini
  added stiffness to karts.ini (stiffness of wheel springs)
  added coast_rate to karts.ini (slowdown when coasting)
  moved translation to the viewport (incomplete)
  changed break_rate to brake_rate (spelling)
  simplified trackscene
  commented out the drawing of red boxes
  changed the default tile for circleofstrif.tmx