Make gitlab shortlinks clickable
Commits for review are at: https://gitlab.gnome.org/3v1n0/gnome-terminal/commits/parse-gitlab-shortlinks (here to compare).
Basically with this branch, shortlinks such as GNOME/gnome-terminal#31
become clickable and copyable in gnome-terminal.
Also, cleaning up a bit the matching code, so that copying a mailto:foo@bar.baz
only copies the actual email address (as the context menu states) now.
It would be easy to support also regex for well known projects like xorg or wayland from fdo gitlab, but didn't want to add too much clutter.