Implements colours and kill option

- random coloured orbs released on mouse click
- rotating kill block will kill stationary orbs of the same colour
- select kill block colour with LEFT and RIGHT arrows

Note: visual layout still intentionally simple.

KNOWN ISSUES -
Blocks become stationary on collision, they will always attempt to move
closer to planet but some collisions are creating overlapped blocks,
this means block may become stuck in mid air as its attempts to move
towards the planet do not release it from its collision state.