Enabled JS support for A*

This moved the majority of the A* plugin files to the Assets/Plugins folder, which more closely matches our project organizational structure. A* editor files are still (frustratingly) located in Assets/AstarPathfindingEditor because the path is hardcoded into the plugin.
Rename AstarAI class to PathfinderAI class.

Pathfinder is a more descriptive name of the class's function.
Removed A* example files from project

- If we want to view the examples at any point, we can always reimport them from the package, but we shouldn't check them into version control.
Refactored CameraController

- Renamed clampPosition to ConstrainPositionToScreen - a more descriptive (and properly capitalized) method name.
- Added comments
Commented SceneController
Refactored Firearm

- Renamed randomRecoil to RandomRecoil
- Added comments
Added comments for Projectile classes
Removed the PickupCollisionHandler

- We're not currently using it, and it wasn't general enough to be useful for now.
Added comments to physics classes
Refactored the Inventory and InventoryItem classes
Moved Firearms prefabs to Player/Firearms folder

- The structure more closely matches our organization of the scripts.
Added comments to ReticleController
We still want to construct an inventory even if it's empty
Removed GUIView

- We're not currently using it, and we might end up restructuring how our GUI stuff works anyway. If we need to view it as an example, it's included in our most recent Cooper prototypes.
Refactored PathfinderAI

- Added MoveAlongPath(). It feels better to handle all pathfinding related functionality in the PathfinderAI class than in the EnemyCharacterController. Also allows us to lock down some variables that probably have no business being public.
Removed view-related classes

- We're not currently using any view/animation-related stuff yet, so let's get rid of the clutter. When we're ready to implement animations, there are examples of using the view classes in the Cooper prototypes repo.
Commented and cleaned up CollisionHandler classes.
Refactored state-related classes.

- Any movement/velocity related variables, properties, or methods should be contained within the MoveableObject class.
- Make Die() an abstract method to be overridden by the subclass.
Added ReticleController.MoveBy()
Added additional method signature for MoveableObject.Move().

- Removed MoveableObject.AddVelocity(). Currently unused.