Removed the old GenerationRule model.
Added a field to store minimum time between turn generations on GenerationTime.
Removed the code from GenerationTime.next_time.

Ultimately, we'll want it to use dateutil's utilities for operating on recurrence rules.
Added new GenerationRule model.
Merge branch 'master' into recurrence

Pull in the tox setup.
Added python-dateutil to the tox dependencies.
Removed commented-out code.
Provide a dict of all available turngeneration plugins.
Rewrote the generation tasks.

Now split into timed_generation and ready_generation.
Added bailout cases to the ready_generation task.
Reimplemented GenerationTime.next_time.
Renamed GenerationTime to Generator.
Fixed a comparison between aware and naive datetimes.

All calculations should be done with naive UTC datetimes.
Moved tests into their own package.
Added the plugin lookup to the tasks.
Rewrote the get_owner method of the views to use our plugins.
PauseView now works.

With tests.
Added actual POST calls to some of the pause tests.
Added UnPauseView.
Changed UnPauseView to check for has_unpause_permission.