Contact classification interface

Submitted by Mikhail Zabaluev

Assigned to Telepathy bugs list

There are cases in which it is useful to distinguish classes of contacts within one connection for UI purposes.

These include:

Undisclosed callers in Skype: The handles can be made unique (no idea yet if Skype can reuse the temporary contact IDs), but the ID is meaningless and should not be displayed.
Undisclosed callers in telephony: coming from a pseudo-contact because it's too weird to have a call with nobody in StreamedMedia (the new Call channel could help with that). The pseudo-contact could be one for all anonymous calls or unique per call, but there is no meaninful handle ID either way, and relying on the CM to supply special case display labels for the UI is bollocks.
Emergency communications: it's useful to see that a contact resolved by regular mechanisms (e.g. by requesting handle "112") is in fact an emergency contact.

There should be an interface and a contact property to obtain contact classes or "tags".