Finished Refactoring StripeController

Created a "SumoTextService", "NotifierService", and a "StatService" class.

NOTE ON "SERVICES": These services are to help us decouple the details of actions we want to call on classes, and in particular models. This also allows us to isolate instance creation and potential meta-actions into a single class for any given model or class.

Additionally, I refactored the WebhookAction class, and have completed refactoring the StripeController in this iteration.

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