tracker: make things fully asynchronous
tracker: make things fully asynchronous

Avoid blocking main loop while parsing results.

Signed-off-by: Lionel Landwerlin <9463032a5b99ffad10f36631678a833369a311b5@linux.intel.com>
Signed-off-by: Juan A. Suarez Romero <af79b5692270b306571bb1d8bbe0285ae3ac93d9@igalia.com>

MathieuDuponchelle/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,grilofw/grilo-plugins,MathieuDuponchelle/grilo-plugins,vrutkovs/grilo-plugins,grilofw/grilo-plugins,vrutkovs/grilo-plugins,vrutkovs/grilo-plugins,MathieuDuponchelle/grilo-plugins,GNOME/grilo-plugins,kyoushuu/grilo-plugins,GNOME/grilo-plugins,kyoushuu/grilo-plugins,jasuarez/grilo-plugins,kyoushuu/grilo-plugins,vrutkovs/grilo-plugins,MikePetullo/grilo-plugins,jasuarez/grilo-plugins,MikePetullo/grilo-plugins