Add contacts to organization

This adds a *Primary Contact* selection to the organization as well as an *Account Manager* on the staff side. 

The account manager can
  * be automatically assigned to all organization tickets
  * be notified of new tickets from the organization
  * be notified of new messages from the organization

The primary contacts can
  * be added automatically as collaborators to the ticket

All organization members can
  * be added automatically as collaborators to the ticket