[BUGFIX] group manager does not have access to ModelsController#timeline

Squashed commit of the following:

commit d205af7a467fd6bb4c6d9cb8c778a53b4ac429dd
Author: Matus Kmit <matus.kmit@zhdk.ch>
Date:   Thu Oct 2 17:20:34 2014 +0200

    test prepare

commit 4d02c557f37d121a4ea7997dafd7a558288996ac
Author: Matus Kmit <matus.kmit@zhdk.ch>
Date:   Thu Oct 2 17:17:11 2014 +0200

    refactor admin check in required role

commit 4bf4d75b9839722e9431ab1a7c3bae6f9a11613c
Author: Matus Kmit <matus.kmit@zhdk.ch>
Date:   Thu Oct 2 17:09:50 2014 +0200

    fix