EVENT-134

- allow registrants to pay any amount (above minimum deposit) at registration time
- condense logic from 3 pages into 1
  - register page when completed and payment page now all handled by reviewRegistration
- easily allows for registrants to make multiple payments of different types (addresses the heart of EVENT-95)
- reviewRegistration page now matches styling of the rest of the registration process
- layout of payment fields adjusted (stacked) to have a nice "line of completion" even on non-mobile devices
- some section headings updated
- guiding/clarifying text added in some areas