Refactor Zencoder related code (prep for ansible)

Squashed commit of the following:

commit d9c6b6ec7fd3566903ec102ea6faba5ea7386a8e
Author: Thomas Schank <DrTom@schank.ch>
Date:   Fri Aug 15 09:47:11 2014 +0200

    Revert "An another level config file for zencoder"

    This reverts commit fc8c39eb5e0b422b6a42ad5e81ef432e5e1e5101.

commit fc8c39eb5e0b422b6a42ad5e81ef432e5e1e5101
Author: Thomas Schank <DrTom@schank.ch>
Date:   Wed Aug 13 15:15:53 2014 +0200

    An another level config file for zencoder

commit 9c2e54b1b08ddd33e4446f4cededaf2285e26b15
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Aug 12 15:48:22 2014 +0200

    More zencoder test fixing

commit 283bd0400605f1c0a8bc9c429fa969fa1a8a1095
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Aug 12 15:42:36 2014 +0200

    Set and adjust zencoder config file for testing

commit dc7582200f5608724fd6e2998b29068c0624c29b
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Aug 12 14:40:50 2014 +0200

    Syntax fix

commit 36af299717ba089eec6c8551d403e6c93f2668c6
Author: Thomas Schank <DrTom@schank.ch>
Date:   Tue Aug 12 14:21:07 2014 +0200

    Cleanup and simplify zencoder configuration
Admin interface: context improvements

Squashed commit of the following:

commit 30d2e50026544bdb52873387ab2a729a9998dd56
Author: Michał Podlecki <m.podlecki@op.pl>
Date:   Fri Aug 8 10:18:37 2014 +0200

    Admin interface: show context's related media sets on a separate page

commit eb9ea2d9bfecc15f77048db61365ca306699e0e7
Author: Michał Podlecki <m.podlecki@op.pl>
Date:   Fri Aug 8 11:54:08 2014 +0200

    Admin interface: ability to edit contexts's description
Admin interface: links between meta keys and contexts