Restricted users (#4334): initial implementation

* Add User.IsRestricted & UI to edit it

* Pass user object instead of user id to places where IsRestricted flag matters

* Restricted users: maintain access rows for all referenced repos (incl public)

* Take logged in user & IsRestricted flag into account in org/repo listings, searches and accesses

* Add basic repo access tests for restricted users

Signed-off-by: Manush Dodunekov <manush@stendahls.se>

models/fixtures/collaboration.yml

@@ -14,4 +14,10 @@
   id: 3
   repo_id: 40
   user_id: 4
-  mode: 2 # write
+  mode: 2 # write
+
+-
+  id: 4
+  repo_id: 4
+  user_id: 29
+  mode: 2 # write