Subscriptions

The following new features:
* Table Listing of Payments for the admin to see charges
* Event handling of succeeded and failed charges
* Implementation of user account lockout when charges fail

Could not get stubbing of responses that StripeEvent makes of Stripe to work.

I would suggest doing your best to avoid making another instance variable here. If you need to have it then you can set it in the `initialize` method. But don't add instance variables in methods unless it is clear in the method name you are going to do that.