Add basic support for multiple calendars

A new branch, since the old branch was kinda broken

### What needs to be done:
**Models/Controllers**
- [x] Tests for calendar model (ALL the things, see `models/event_spec` for examples)
- [x] Tests for Event model (should always be part of calendar)
- [x] Make old tests pass
- [ ] Clean up unused files generated by scaffold
- [x] Unique URL token for each calendar
- [ ] Guest user

**Views**
- [x] List of calendars
- [x] Single calendar, accessed via token
- [ ] `calendar#show` should equal the old `events#calendar`
- [ ] `calendar#new` form
- [ ] `calendar#edit` form
- [ ] Integration tests for every view
- [ ] Move list of calendars into partial and include partial in `calendar#show` view
- [ ] Need unique token for each `event` as well

I also imagine there will be a lot of pain with merging it in :+1: 

ref #16