Added slideshow block and CmfMedia

[rmsint]

Can be used to test CmfMedia

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	yes
Deprecations?	no
Tests pass?	na
Fixed tickets	na
License	MIT
Doc PR	symfony-cmf/symfony-cmf-docs#191

To test:

• checkout this PR
• add the MediaBundle and LiipImagineBundle to composer (dev-master)

composer require liip/imagine-bundle symfony-cmf/media-bundle

• checkout these PRs - they need to be merged first, before this PR can be merged:
  • CreateBundle media-bundle#27
  • Update ImagineBlock to use CmfMedia image block-bundle#72
  • Removed image document doctrine/phpcr-odm#293
  • Removed all image code doctrine/DoctrinePHPCRBundle#72
  • Update to use CmfMedia Image create-bundle#60
• checkout the following packages to the latest master:
  • phpcr/phpcr-utils
  • sonata-project/admin-bundle
  • sonata-project/block-bundle
• run app/console doctrine:phpcr:repository:init - creates /cms/media