Destroy media_file and actual files when media_entry is destroyed

Squashed commit of the following:

commit fd023bbcf07a7c453bdb5e91e25d294c810d1992
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Jul 22 14:25:01 2013 +0200

    Added feature test for deleting a media_entry, media_file and actual file

commit aae395ca07360d2c6fb413e8c71215f543482b68
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Jul 22 10:20:32 2013 +0200

    Use destroy instead of delete in relation

commit e0885da3e81268141efe9b8880d0d549e6bb5383
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Jul 22 09:15:49 2013 +0200

    Try to fix eager loading

commit 36d03c759f8cb686f84cceb88c837b0d86fee4d2
Author: Thomas Schank <DrTom@schank.ch>
Date:   Mon Jul 22 09:10:48 2013 +0200

    Reverted eager loading of files for media_resources

commit ab14f5c40a7242b6cf26a549c3cc36c392ba322c
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Jul 19 17:03:56 2013 +0200

    Try to reenable eager loading with includes

commit 18a491dc019bcaf546a1c258072d2affe0662279
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Jul 19 14:03:13 2013 +0200

    Dependent delete for media_resource to media_file, use after_commit,  and a fix

commit 5e6108a07525994559e1e0dbee812040b0231867
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Jul 17 14:07:31 2013 +0200

    Disambiguate select statement

commit 2b4af2331c2d7e07ba479b51c044484b35149be4
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Jul 17 13:42:03 2013 +0200

    Filter MediaEntry instead of MediaResource when we want Entries

commit 19f334d468e4b3aaf30603fa06fddf9d65002389
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Jul 17 13:20:32 2013 +0200

    media_entries of media_resources switches the type in rails aware manner

commit 4eaf00f4898e168d7a14f75463867c350a88c390
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Jul 17 10:22:31 2013 +0200

    Fix removed has_many :media_entries in media_file an one usage

commit a40d47f8f76fd55fd5cc43576230c62b56c8641a
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Jul 17 09:12:12 2013 +0200

    Fix syntax

commit 3e4404d04378270548587c5132d0ccac94fdc030
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jul 16 15:07:21 2013 +0200

    Fix by not using eager loading

commit 44727a929559d25495508695ede58a3d7a7adfa3
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jul 16 13:17:19 2013 +0200

    More fixes

commit 293990db896807f60e59dbdd737ba0b8eb4cce2d
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jul 16 12:17:12 2013 +0200

    Fix?

commit 526f065bc1da68e8b642a908d3d1f332d26b8cf1
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jul 16 12:08:10 2013 +0200

    Migrated contained personas db

commit a598f3d86242af47fd3a1d3b0c05d4faa9af74a4
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Jul 16 11:35:06 2013 +0200

    Reverse media_entry / media_file relation