Admin interface: remove admin users section

Squashed commit of the following:

commit 6ed3d44cec9ecf9f5ae06cdddd66b21bd2951968
Author: Michał Podlecki <m.podlecki@op.pl>
Date:   Thu Sep 11 18:26:05 2014 +0200

    Admin interface: remove admin users section
Add condition for when media resource isn't a media set and doesn't contain a media file

Squashed commit of the following:

commit 9c80dda557725d9d79af826d3f0a419c95487dd2
Author: Jonasz Grochowski <tensaioni@gmail.com>
Date:   Fri Sep 12 09:53:27 2014 +0200

    Add condition for when media resource isn't a media set and doesn't contain a media file
Add preloader for pdf reader

Squashed commit of the following:

commit befc128f58fab75287ee1bd886043fdf5bce68c6
Author: Jonasz Grochowski <tensaioni@gmail.com>
Date:   Fri Sep 12 11:02:47 2014 +0200

    Add preloader for pdf reader
Add legacy media_entries and media_set routes