Payments

admin UI for payments: 
- [x] dashboard link to create new
- [x] ability to associate payment with any Payable object

user UI for payments:
- [x] listing of payable events
- [x] correct scoping of payable events
- [x] ajax submission of payments
- [x] ajax auth with stripe

- [ ] Admins should be able to mark payments as paid so each user should have "open payments" that an admin can check off if paid out of band. 
- [ ] Receipts via email for all payments and available for download as PDF.
- [ ] Recurring payments for dues?