[Feature] Improve user roles view

[Exotelis]

When editing a user roles, the user should be redirected to an overview page but not to the edit form. By clicking a button Edit or Update the preview mode should switch to the form view.

In addition, the user should see a list of users that are assigned to this role. The user should be able to move users from this role to another to remove all users, one by another, from this role, to be able to delete the role. It might would make sense to have a bulk move operation.