[WIP] Seo bundle integration

That's the next try to insert SeoBundle into Sandbox. There are still some issues i need to fix:

* [x] created a fix PR on SeoBundle for that
* [x] titles for non seo content https://github.com/symfony-cmf/SeoBundle/issues/75
* [x] admin extension https://github.com/symfony-cmf/SeoBundle/pull/53
* [x] two different examples, one for using Admin-Extension (`SeoAwarecContent`) and one for the Extractors