Added a skybox i found online (not good..)

http://www.3delyvisions.com/skf1.htm
Signed-off-by: Kalle Sjöström <c06ksm@gmail.com>
Added concept of "Pusher" in movers.

Now some movers can be "Pushers". This is set in the editor as a check-box. This means that it will try and push away others while moving. The player unit has it by default, but normal boxes can have it too so the pushes can be "chained".

Signed-off-by: Kalle Sjöström <c06ksm@gmail.com>