Handle external links in PDFs
Handle external links in PDFs

Evince provides a signal for this, all we need to do is connect to it and
use Gtk.show_uri().

https://phabricator.endlessm.com/T12577

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib