[FIX] Paramater manager bug in abstract checking
[MIN] Removed unnecessary table tag
[FIX] StopIteration error on deleted fields

 * Causing issues on abstract accept
Do not show participation acc/rej form if sent

Once the user has accepted/refused the participation invitation
showing the form again resulted in a not very helpful error message.
Instead we now tell the user that he already accepted/rejected the
invitation.
Apply the same check on the reject-only form
Add missing i18n to participation "error" messages
[FIX] Registration HTTP API permissions
[REF] RegForm: mandatory event validation
[FIX] RegForm: Validation for section dialogs
[FIX] RegForm: SocialEvent Accompanying validation
[IMP] RegForm: validation enabled for ng-table
[IMP] RegForm: Section config dialog validate tab

Atomatic selection of the tab containing validation errors will only work from Angular 1.2 onwards
[FIX] RegForm: SocialEvent config frontend valid.