telepathyClient: Gracefully handle missing telepathy deps

telepathyClient: Gracefully handle missing telepathy deps

Telepathy's role has been diminishing continuously over the last
couple of years, so while chat integration is a nice feature for
those who use it, it is hard to justify keeping it as a hard
dependency. To address this, split out the component from the
client so we can handle missing typelibs gracefully by not
providing any chat integration.

https://bugzilla.gnome.org/show_bug.cgi?id=779878