Simplify _pick_best_resource.
Simplify _pick_best_resource.

The previous logic had some ... interesting features, like assuming that
anyone who speaks modern Jingle understands audio and video. This is
somewhat more straightforward:

 * Try modern Jingle;
 * Try Jingle draft 0.15;
 * Try GTalk 0.3, with video if appropriate;
 * Try GTalk 0.4.

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