Many many bugfix

- closes #43 
- Facebook URL field no longer manditory
- Google Calendar errors now render as a toast, instead of internal server erroring
- fix a few logical bugs for what events show up where
I think this could be made simpler by defining [`__eq__`](https://docs.python.org/2/reference/datamodel.html#object.__eq__) for [`TimeField`](https://github.com/danrschlosser/eventum/blob/fix_event_errors/app/models/fields/TimeField.py)