[meta] User management and Subgroups

This summarizes the conclusions of a conversation I had with @dzaporozhets.

We want to make it easier to manage permissions and projects in GitLab. To do that, we want to introduce the following changes, in this order:

Considering the demand for these and other big architectural changes, we're hoping to schedule GitLab 9.0 for this year (lets say November, for DZ's birthday).


cc @dzaporozhets @markpundsack @stanhu @sytses