Allow to set abilities when assigning responsible users

[patrickrobrecht]

Users responsible for an organization may be given the ability to

• create events for the organization
• create event series for the organization
• upload documents to the organization
  even if they do not have the global right to do so.

Users responsible for an event may be given the ability to

• create child events
• manage booking options
• view bookings
• edit bookings
  even if they do not have the global right to do so.

Users responsible for an event series may be given the ability to

• create child event series
• upload documents to the event series
• create new events within the event series
  even if they do not have the global right to do so.