added add/remove functions to register and remove creeps from each wave

Signed-off-by: Spyros Gasteratos <morfeas3000@gmail.com>
added the explode function in a particle which can be used for collisions

Signed-off-by: Spyros Gasteratos <morfeas3000@gmail.com>
Merge branch 'master' of https://github.com/northdpole/scaling-happiness
added grid

Signed-off-by: Spyros Gasteratos <morfeas3000@gmail.com>