group: set priv->setting_value to TRUE when moving ourselves

in _child_removed.
Merge branch 'integration' of https://github.com/MathieuDuponchelle/PitiviGes into github-mathieu/integration
integration: add seek argument to test_timeline_with_profile

Needed for seek tests. Other users of the function can specify 0.0, meaning no
seek is requested. _seeking_playback is also changed to accept a seek argument.