CreateBundle

The parts removed in the create PR https://github.com/symfony-cmf/CreateBundle/pull/60 are added in this PR.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | na
| Fixed tickets | 
| License       | MIT
| Doc PR        | https://github.com/symfony-cmf/symfony-cmf-docs/pull/191

**TODO to merge**:
- [x] rename EditorHelper -> UploadEditorHelper and rename FileUploadHelper -> UploadFileHelper
- [x] update + check MediaManagerInterface docblocks (use ``@see`` anotations to mark relations with Sonata)
- [x] ``Doctrine\Phpcr\MediaManager``
  - add issue ticket to TODO note about the phpcr autoname
  - update $rootPath check in the mapPathToId method
- [x] serializer handler
  - change the method name, include the media name field
  - create an issue for further improvements discussed (reference it in a comment in the code)
- [x] add more docs to ``UploadEditorHelperInterface``
- [x] ``ImageRepositoryInterface:: getImagesByName ``: change to ``searchImages($term, $limit = 0, $offset = 0)``
- [x] move security checks from create to ``FileController::uploadAction``
- [x] squash commits once its all cleaned up - the history will be easier to understand if this refacotring is one big commit