ReRefactor reservations controller

[squidgetx]

The reservation controller is absurd. We should move out most of the logic to model instance methods; the only logic in the controller should be related to param parsing or whatnot.

At the same time make sure that tests migrate to the model appropriately and also write tests for approve/deny.

[shippy]

While I agree that most of the code should be refactored out, I wonder if tests should remain where they are. Controller tests verify overall functionality of the action / are mini-integration tests; consequntly, they should catch interactions even if the logic is executed elsewhere. But that leads to some duplication. Thoughts?

[squidgetx]

Waiting on #863. We can keep tests in the controller spec (I didn't get to move out as much code as I wanted, in the end..)