JingleSession: localize use of peer handle.
JingleSession: localize use of peer handle.

Now that we only use a handle in one place, let's move everything to do
with it there.

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