[1.0][loader] cleanup filesystem loader, simplify logic, add factory.

[makasim]

This PR removes some config params: formats and data_root. Adds a factory so now we can configure several filesystem loaders.

liip_imagine:
  loaders:
    default:
      filesystem: ~
    foo:
      filesystem:
        data_root: %kernel.root_dir%/../web

The logic is working, still have to add and fix some tests.

[makasim]

@havvg ready. This PR simplify FileSystemLoader logic. Now it does not do any assumptions on the given pass. It does not guess the format or directory etc. Just adds correctly the path to the data_root configured.

This may not satisfy somebody, that's why I waiting for your approve. WOULD really like to get it (:

[psytraxx]

@dbu - i have serios troubles to get this working with data_loader: cmf_media_doctrine_phpcr - is there a problem on my side or is this not implemented yet ?

An exception has been thrown during the rendering of a template ("Could not find resolver for "cmf_319_179" filter type")

    #blog teaser image
    cmf_319_179:
        quality: 80
        data_loader: cmf_media_doctrine_phpcr
        filters:
            thumbnail: { size: [319, 179], mode: outbound }

[dbu]

@psytraxx you should probably open a new issue for that. i don't know what the state is, but the cmf is only tested with the 0.9 branch of LiipImagineBundle, not the 1.0 so it could be that this was broken at some point.

would of course be good if somebody can set up tests that we see such issues immediately.