Map ids (uuid, int, url-string) in media_resources#index to uuids

Squashed commit of the following:

commit 4444d0580a528a1471320aaf6b43f08dbecba043
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Apr 4 14:39:46 2014 +0200

    Move to appropriate module name and use in the filter_opts

commit 199ee24899c99185acbf71d9bf1c29027617c9da
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Apr 4 14:31:27 2014 +0200

    Implement media_resource id convertor in  Concerns::MediaResourceId