Elevator control

[SPCOxion]

Throwing a position control PD loop at it will probably work well enough for what we want to do.

[SPCOxion]

Instead of a PD loop, it's probably better to use a P loop with feed forward. Since the elevator motors are geared so high, the feed forward value very well may be 0.

[SPCOxion]

Added in the Elevator branch. Needs to be tested before merging to master.