grilo: Use popover for the source selection

https://bugzilla.gnome.org/show_bug.cgi?id=723031
libgd: Update from master

To get the gd_tagged_entry_tag_get_area() function.
opensubtitles: Fix indentation

Spotted by Ignacio Casal Quinteiro <ignacio.casal@nice-software.com>
grilo: Start implementing search source removal