Implement 3D physics library

[NBT22]

Actors should be able to exist within a pseudo three dimensional world by having the concepts of height and gravity.

[NBT22]

Closely related to #48

[droc101]

we are going to use a full 3d physics engine to replace box2d.
considerations:

• model transform matrix will need to have 3d rotation
• add looking up/down
• collision for floor and ceiling must be accounted for on all actors, not just ones within range of the floor quad or something

[droc101]

could use something like jolt physics (which has c bindings available)

[NBT22]

We have chosen to use Jolt Physics and the joltc bindings. As Jolt does not have any sort of navigation system built in, we will either implement a cell-based A* algorithm or use a library for navigation.

If we choose to implement our own navigation system it could potentially be more refined, due to a knowledge of the constraints which are placed on level creation (such as having special handling for a sloped sector rather than just using cells).