[#81588990] Overbooking should not be possible for group managers
[#81588990] prevent overbooking from group_manager

Squashed commit of the following:

commit b3c7a189cb7a197b74c54c78dcc5b7f0c25e5edc
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Fri Nov 7 11:08:42 2014 +0100

    [FIX CI]

commit 472faa5cdcd5b1a169fab222375aac5d142f6a81
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Thu Nov 6 15:50:34 2014 +0100

    fix within wrapper

commit 712742dedc4655822f48b40fbbd75362c5fb6f50
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Thu Nov 6 15:24:43 2014 +0100

    regenerated yaml for cider with firefox as default browser

commit d0c697bd9ebb0f66a11526542352ffcd51fd2dcd
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Thu Nov 6 15:14:09 2014 +0100

    scenarios yaml

commit 5d712ccedb01e9ff595047a58163c6b408477bbd
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Thu Nov 6 15:12:15 2014 +0100

    just wrapping in within

commit d1bcc7afef40ace512977d121e082d3ba041c8f0
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Thu Nov 6 14:52:29 2014 +0100

    try on CI

commit 83c583af050e4fdeb78c6332bb2ebaa2a23cc878
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Thu Nov 6 14:47:16 2014 +0100

    [FIX CI]

commit 94d2a0bbe7d0dd9ac2dc5089e2d067b4845c62a4
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Thu Nov 6 14:20:07 2014 +0100

    [FIX CI]

commit 8e19c512c7aae93c185d0db6d32743094b7cb365
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Wed Nov 5 12:52:53 2014 +0100

    [FIX CI]

commit 56c43443b5c4f8551d19d129bd9d72f08edbf7dc
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Wed Nov 5 12:22:43 2014 +0100

    regenerated yaml for cider with firefox as default browser

commit 0ab894ecf9853b1c88208a57c8429794644fc69e
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Wed Nov 5 12:01:50 2014 +0100

    regenerated yaml for cider

commit 8db4e0b1dab1702688c25114b7abd9194b759a8e
Author: Franco Sellitto <franco.sellitto@zhdk.ch>
Date:   Wed Nov 5 12:00:59 2014 +0100

    prevent overbooking from group_manager