GitLab

This should cause all patches submitted using git-phab to be assigned to
the #libnice project for review, by default.
Signed-off-by: Philip Withnall <philip@tecnocode.co.uk>

This fixes `arc diff` to select the right repository when submitting
patches.

This completes the transition to Phabricator; everyone should be using
the same project settings now.

https://phabricator.freedesktop.org/tag/libnice/