utils: function remove_underscore_keys removal

* Removes unused function `remove_underscore_keys`.

* Improves PEP8/257 and adds documentation entry.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
multimedia: image: API

* Introduces image API with `resize`, `crop`, `rotate`, `format` and `quality`
  functionality.

* Introduces image cache object via redis.

* API testsuite.

Signed-off-by: Harris Tzovanakis <drjova@cern.ch>
multimedia: image: IIIF Image API

* Implements the IIIF Image API.

* NOTE: For more info please read <http://iiif.io/api/image/2.0/>

Signed-off-by: Harris Tzovanakis <drjova@cern.ch>