Feature/quarterly yearly recurrences

This pull request:

- Removes sub-recurrences. They were needlessly complicated and not fitting with the core use case of localized recurrences.
- Fixes a bug where monthly recurrences at the end of the month could throw errors.
- Adds Quarterly and Yearly recurrences as options.
- Cleans up tests to use django-dynamic-fixture and removes tests that were testing django behavior (such as testing that a model is saved)