Use ordered timespans to prevent data separation.
Simple editable reservations. WIP.
Add editable reservations for recurrences.

Disable them for groups and manually approved reservations.
Add method to be able to overwrite functionality.
Fire events when modifying reservations.
Send mail notifications on reservations update.
Only send notifications when data changed.
Update french translations.
Update translation.
Merge branch 'deif-editable-reservations'

Conflicts:
	seantis/reservation/reserve.py
Fix tests.
Fix tests.