Add basic support for multiple calendars

A new branch, since the old branch was kinda broken

What needs to be done:
- [ ] Tests for calendar model (ALL the things, see `models/event_spec` for examples)
- [ ] Tests for User model (calendar creation)
- [x] Tests for Event model (should always be part of calendar)
- [x] Use FactoryGirl for setting up objects in the model specs
- [ ] Make old tests pass
- [ ] `calendar#show` should equal the old `events#calendar`
- [ ] Integration tests for views
- [ ] Clean up unused files generated by scaffold

I also imagine there will be a lot of pain with merging it in :+1: 

ref #16