bookmarks: Fix content-added signal for new items
bookmarks: Fix content-added signal for new items

We want to tell the front-end about the newly added item, not that
we added the parent container.

https://bugzilla.gnome.org/show_bug.cgi?id=724548

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