Merge pull request #323 from BU-CS673/pmd3

Pmd3 -> Production: Bullet collisions & tree growth
Corrected DrawLayers, fixed most Tank tests

DropPillbox and DropMine tests still failing.
Revert "Corrected DrawLayers, fixed most Tank tests"

This reverts commit 25f5f7fdf53bcb069e51149eecd4797ee2c8df3c.
Merge pull request #335 from BU-CS673/production

Production