sflphone daemon can not work without DBus

Those are the versions in last Ubuntu LTS

refactor while we're at it

Since we support old GTK versions (2.20 on lucid), supporting GTK3 as well
will be quite invasive and ugly

fixes regression from 561492a9

Caused by double free.

More pervasive changes were just to fix "transfert" typo

same fix than [1519fc4d], for transfer button this time

Fix a deadlock when closing the error dialog
Remove unused functions