Jetpack functionality

[pizzatree]

Check on server if available thrust
If so, ask server to add upward velocity to player rigidbody

[pizzatree]

Partially added in 9a48b32
Needs

• Server authorized thrust limit
• To be powered by a formal inputs class (don't want it hardcoded)
• Sound effects, particle effects
• Better values for the physics to make it actually feel good
• Possibly a sputter up when you run out of thrust?