Minor fixes

- wrong spelling of "occurrence"
- using [] instead of get() when get functionality is notn eeded
occurrence is_sent when modifying daily repetition

Bookings with daily repetition only get one notification, and this is
done by setting is_sent for all occurrences. When modifying such a
reservation we need to update the new occurrences accordingly.
Add ReservationOccurrence.is_rejected
Remove lots of obsolete code
Improve display of occurrence cancel/reject reason
Remove skip conflicts checkbox

We always show conflicts so having the checkbox does not make much sense
Fix invalid argument usage when cancelling
Start time changes should not revive occurrences
Remove the dangerous CreateTables config option

It does not only create tables but actually delete everything first.
There's no good reason to keep such a setting around.
Fix some data not being saved in jstorage
Allow going back in the 3-step booking process
Fixed unpacking with too few arguments
Don't show blockings in booking quick searches