core: support transform GValue to key's GType
core: support transform GValue to key's GType

Although some conversions might imply losing precision, there is a
major gain over situations like deserializing data.

APIs that might be affected by this are the ones handling GValue as
argument. In grl_related_keys_set() is where the code rely on checking
the GType and failing if needed.

Signed-off-by: Victor Toso <39b7599ff73bbf5db531748ba5250f21fa7120ff@gnome.org>

jasuarez/grilo,grilofw/grilo,grilofw/grilo,jasuarez/grilo,jasuarez/grilo,GNOME/grilo,grilofw/grilo,GNOME/grilo