Post-WIP fixes

- Remove Room.getRoomsOfUser - Room.find_all(..) is just as good
- Some indentation and i18n in blocking templates
- Add Reservation.details_url and use them in the rejection emails
- Renamed indico.modules.rb.notifications.blocking => .blockings
- Fix messed-up blocking form RH class name
- Migration: Cancel occurrences of cancelled/rejected reservations
Fix a somewhat cancerous function name
Make sure __repr__ returns plain ascii

This is done by decorating all __repr__ methods with @return_ascii and
returning an unicode string. That way creating the representation works
fine (the values are unicode after all!) and then the decorator converts
it to plain ascii. To get a nicer result: 'pip install translitcodec'
Much nicer enum handling using enum34