Configurable contexts in list-views

Squashed commit of the following:

commit c54d266065cdf26da05a205b1752200e9013ec12
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Jun 19 09:56:06 2013 +0200

    Displaying context

commit 71c9b21d74b03d12ba43c6bf3c6e4dc0baa6d702
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Jun 19 09:24:32 2013 +0200

    Add window.AppSettings object; Revert initializing MediaResourcesController.Index

    This reverts commit 8bff2fdf562c45aa9cc26fc7b1413901125f1847.

commit baa62c1c4004090df5d912b902ac3a6fc8c228ae
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 14:01:05 2013 +0200

    Setting data attribute for contexts to true

commit 8bff2fdf562c45aa9cc26fc7b1413901125f1847
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 13:12:43 2013 +0200

    Loading app_settings in before filter; initializing MediaResourcesController.Index with it

commit e1e3753b0e0a146204ddace918f52e9e9343d607
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 10:00:55 2013 +0200

    Added configuration of second and third displayed meta_context

      to the app_settings admin interface

commit cdeb211c02d8b7ebf7c26cfac09f319dd3bca046
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 09:30:10 2013 +0200

    Add displayed_meta_contexts to app_settings

commit 7a62f8c54f9f42b61435efdeac35bdd938adf214
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 12:11:59 2013 +0200

    Railguard MetaContextName fixing

commit c6ca20f96d40b7681f4282b7c6f74c7ab7639826
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 11:09:30 2013 +0200

    Railguard MetaContextName fixing

commit eb515a24fd296237d93e27d92afd2829c24d1ff1
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 10:34:51 2013 +0200

    Railguard MetaContextName fixing

commit 244fcba1055559c7b6e393bc56c717536393b796
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 10:31:22 2013 +0200

    Railguard MetaContextName fixing

commit d9c081eb07f7ca50c1b9c6d1fc2e8e88f36c7f7b
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 10:11:34 2013 +0200

    Railguard MetaContextName fixing

commit 9e26f11e38f82949838b898e55a4900f1ede7328
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 09:30:37 2013 +0200

    Railguard MetaContextName fixing

commit 938b54eaefec84b6d69f02ceeac0a92224d0a78e
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jun 18 09:09:29 2013 +0200

    Refactored meta_context_id to meta_context_name

commit 8f0b5f79897743c7d8167f122e6dd034da952a74
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Jun 17 14:29:59 2013 +0200

    Fixing a query that used the removed meta_contexts.id

commit f6382d24896b5310a9fdfab7885af021cad0ad76
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Jun 17 14:27:07 2013 +0200

    Using name as pkey of meta_contexts