Users can become inconsistents

[StCyr]

users can be members of several workspaces but we keep a list of a workspace's members in every workspace. Hence, users accross these lists can become inconsistent (eg: a user listed in workspace A can have its groups property containing 'groupA' and 'groupB', while the same user listed in workspace B can have its groups property containing only 'groupA').

Code refactoring may be needed to treat users as first-class objects, the same way we treat workspaces