Fix Imagine Adapter due to last ImagineBundle commits

Hi guys,

I had some troubles to implement an ImagineBlock, this is due to last commits on LiipImagineBundle which change some namespaces.

This PR fix it.

Thanks

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

- [x] fix the tests as they have not been updated yet
- [x] submit changes to the documentation