Add support for gitlab shared groups

[FredCoen]

In GitLab a group you can have members of another group.
https://docs.gitlab.com/ee/user/group/#sharing-a-group-with-another-group

Support for having all members available in the GitLive Team window.

For example:
You have a group developers that contain all the developers of your company.
And you have a group Acme which is the client.
In the Acme group you have a few members ( the product owner, their CEO, whatever )
And in the Acme group we also invite the developers group. So all our developers can work on projects of that group.
Without having to invite each member individually.