[FIX] Don't show "Modify" button for cancelled bookings

 * nor rejected ones
[FIX] Back to proper angular submodule
[FIX] Run scheduler within Flask app context
[FIX] RegForm: Disabled cache for IE
[IMP] i18n dictionary updates

 * Performed by Pedro
[FIX] typo
[MIN] Clean URL for material in subcontribution
[FIX] some missing mathjax js
[FIX] RB timebar image url
[MIN] Prettier URL for chatroom logs
[FIX] Check group exists in LDAP
[FIX] Destroy qTip when parent element destroyed
[FIX] Properly render MathJax sub-titles
[IMP] PendingNotification inherits from Generic
[FIX] Added RB SASS in conference RB
[FIX] RegForm: Full display page exception
[FIX] Missing endpoint for registration services
[FIX] Active tab overrides hidden/disabled state

This is necessary to avoid JS breaking the whole page if a static tab
control is displayed but its active tab does not exist (because it's
hidden or disabled)
[FIX] Weird roombooking button logic

- Delete should be shown even if the booking is rejected/cancelled
- There is no point in cancelling/rejecting occurences for a
  rejected/cancelled booking
- Some refactoring of the code (still ugly, but not as ugly as before)
[MIN] s/exiting/existing/