[FIX] Deletion of VS triggered

- When a Contribution or SessionSlot is deleted
[FIX] Merge API keys

More recent one is preserved if both users had one
[FIX] categ manager email when adding egroup
[FIX] Add canModify to SessionSlot
[FIX] HTTP API canModify in CSBookings
[FIX] Social events check selected
[FIX] RegForm: Ensure no unicode is stored in db
[MIN] Some PEP8 love

 * OmeGak
[FIX] Don't modify list while iterating
[FIX] Bound method Abstract Management
[MIN] Added bookedForId to getReservations
[IMP] Render MathJax on event pages
[FIX] canModify filter for HTTP API
[FIX] SessionSlot notify deleted
Merge branch 'master' into v1.2
[IMP] Timetable: Weekly view
[FIX] Deletion of Evaluation Alarms
[FIX] Category materials sorted
[IMP] Adapt material editor for categories
[IMP] Material listing in Category Display

- Some PEP8 fixes
- Closes #1468