telepathyClient: Don't conflate network- with account changes

On startup, we need to pick up both the initial network status
as well as the account status (so we identify the user and
connect rooms when the account is already connected, for
example when restarted after a crash). We currently cover
both cases when handling changes to the network availability,
however as we are about to monitor more network changes, we
may end up reinitializing accounts that are already connected.
While that shouldn't break anything, we can avoid the unnecessary
work by handling network- and account status initialization
separately.

https://bugzilla.gnome.org/show_bug.cgi?id=784047