[WIP] Fixed bugs when Symfony is not in the root

This fixes the CKEDITOR when Symfony is not installed in the root.

There is one thing left:

 * [ ] The link to the createbundle.png file is absolute, so it doesn't work. However, we can't use twig's `asset()` function in a stylesheet.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -