Add and use media browser

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | https://github.com/symfony-cmf/symfony-cmf-docs/pull/251

** Installation**
- install ckeditor according the create documentation
- follow installation instruction added in https://github.com/symfony-cmf/symfony-cmf-docs/pull/251

**TODO**

- [ ] add cookbook article about integrating CmfMedia with ckeditor and elfinder for both Create and admin forms (CKEditorBundle)