Flatten _emit_capabilities_changed into _emit_contact_capabilities_changed
Flatten _emit_capabilities_changed into _emit_contact_capabilities_changed

In the process, stop assuming that AdvertiseCapabilities will never change
our ContactCapabilities, and that SetSelfCapabilities will never change
our Capabilities.

jku/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,jku/telepathy-gabble