WIP: Add special purpose contacts
First approach to distinguishable contact types:
- Start with four contact types (CONTACT, PRIVATE_MAILBOX, CONTACT_MAILBOX and MAILBOX_OWNER)
- getContacts will only return regular contacts, getAllContacts() will return contacts of every type
- ContactHooks now declare which type of contacts they want to receive.
- Adds a database migration
Edited by Julian Dehm