Better group view with objects ACLs

[olivierlambert]

We can avoid to create another data structure for grouping objects.

Instead, we can:

• modify the group view, with the list of existing groups and a button "Create Group"
• when we click on a group, it displays: members of the group (with possibility to add/remove users) but also the objects "affected" by this group (e.g: authorized VM).

GitLab gives a good example of functional UI for this.

[olivierlambert]

Done with 32642f1