GitLab

This adds a new page to the groups subnav menu where participation
in the group by members and non-members can be viewed by the people
who manage the group.

Change-Id: Icd0603b2bb0f448c0523e8ae12c2fb7c8a5e3d4d
Signed-off-by: Melissa Draper <melissa@catalyst.net.nz>