testing: adding instance of API:Application to the testing database
Enable Thin again (some bugs, but test rum more reliably)

This reverts commit e2e3fad5752f78c8af44d81a99a7a73c931f7a8e.
Fix: create pdf previews during import#upload; test, too

Squashed commit of the following:

commit 42f35fc34d32a14c782548c1ea9b878b05e184fb
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Apr 4 15:03:17 2014 +0200

    Require only 5 pdf-previews

commit d37071f78fdd0850747d4823d2d00770feaa6273
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Apr 4 13:42:44 2014 +0200

    Fix: create pdf previews during import#upload

commit 41f3308ad092f2c07f4fd2e426fa38527248ba05
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Apr 4 13:38:46 2014 +0200

    Added spec for importing a pdf
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