CollidingGroups just saving just the name of group collision solver uses groups by names
Merge branch 'dev' of https://github.com/sunriseJS/sunriseJS into dev

# By JGerdes
# Via JGerdes
* 'dev' of https://github.com/sunriseJS/sunriseJS:
  improved shooter test game
  getGroupsByEntity returns empty array instead of false
  2nd test game: bullets have effect on enemies
  fixed: still problems with alpha (restored state after reset alpha)
  fixed: alpha of canvas wasn't restored properly
  added bullets
  shooter test game uses new animations
  fixed: Renderer didn't rotate around anchor point
  Renderer supports in'n'out animations
  changed background images of 2nd test game
  added bots
  created another test game