Ragdoll enemies on death

[rafaelgonzalez]

• [x] Implement ragdolls
• [x] Make ragdolls avoid collisions with everything except the ground & themselves
• [x] Name enemy bone structure to match Unity's ragdoll bone structure expectations
• [x] Rename player bone structure to match enemy's

[rafaelgonzalez]

Closed in #43