EZP-20831: refactored REST content controller

Changed injection of individual services to repository injection.
EZP-20831: Added ContentImageVariation value object & visitor
EZP-20831: fixed refactoring of controller injection
EZP-20831: Added REST route to get/generate image variation

Route: /content/image/<contentId>/<fieldId>/<variationName>
Example: /content/image/594/12435/small
EZP-20831: Added injection of variants list to ImageProcessor factory
EZP-20831: implement link from Content to ImageVariation
EZP-20831: updated REST specifications
EZP-20831: specs formatting fix
EZP-20831: Changed route name

Integrated remarks by @docb22 about the route + node name in ImageVariation
EZP-20831: s/imageVariationId/imageId/g
EZP-20831: renamed image variations route

/content/binary/images/<imageId>/variations/<variationId>
EZP-20831: Fixed ImageProcessorTest
EZP-20831: Fixed FieldType\Test\ImageTest
EZP-20831: Fixed ImageIntegrationTest
EZP-20831: s/variant/variation/
EZP-20831: Fixed generation of self-href in ImageVariation
PHPDoc on Values\Variation and Values\ImageVariation
EZP-20831: Removed IOService from REST\Controller\Content
EZP-20831: Refactored image variations into a new controller

- Created REST\Server\Controller\BinaryContent
- Added setRepository to REST\Server\Controller so that
  it is available in all controllers
EZP-20831: cleanup