[WIP] started with classes and adapters

I kept everything here to easily try out the interface implementation in classes and adapters etc. The intention is to move them later to other namespaces and bundles. So I started:

- with a gaufrette adapter (also provides easy integration with sonata)
- a LiipImagine data loader (kept as generic as possible)
- to move the Image class from PHPCRODM to here

My idea is to move changes to the interfaces to https://github.com/symfony-cmf/MediaBundle/pull/2 once they are clear.