[WIP] update fallback locales based on request

fix #44 , depends on https://github.com/doctrine/phpcr-odm/pull/445

there is an additional configuration option

    doctrine_phpcr:
      odm:
        locale_fallback: hardcoded
        locales:
            en:
                - de
                - fr
            de:
                - en
                - fr
            fr:
                - en
                - de

* the fallback mode can be hardcoded (do not do anything based on request) or merge to prepend the request locales, or replace to replace the configured language order with the request information.