status should be used to track our presence show value only

All code should depend on ClientState to determine if we are offline

Missing one of these values leads to broken accounts

Fix syntax error

Remove servers which

- Redirect to a website
- Are not reachable
- Have invalid certificates

Dataforms can provide default values for fields

This generates too much debug output

Fixes #10026

GStreamer is an optional package, we can't depend on it beeing imported

Replaced by gtk/dataform.py

This uses the same mechanism originally added for preferences, so that
video display is handled by a GTK+ widget instead of some X11 dark
magic.

This makes the self video display properly (!) during a Jingle call, but
still with random freezes and no remote video being displayed, those
fixes will be for a latter commit.