Collision loop stops at 1st collision for colliders

This means that each projectile can hit one and ONLY ONE other object.
Implemented first version of viewport movement
Fixed bug where enemy bombs were misplaced
temporary solution to our cache struggles
Viewport also (slightly) follows the mouse cursor on X-axis
Closes #25
Merge pull request #72 from Stopa/viewport-changes

Viewport panning
closes #25