Refactored StripeController

Moved all business logic out of the StripeController and into library classes.

The following new classes were extracted:

1. DesignationService
2. GiftService
3. UserService
4. WebhookAction

At this point in time, the refactoring for the StripeController is almost complete. Refactoring will need to be done for the WebhookAction class, which has some hidden dependencies at the current time.

Signed-off-by: Daniel Long <wizazzle@gmail.com>