Merge inn changes / features form symfony standard


Todo:
- [x] Sync existing files (including index_dev protection)
- [ ] Add SensioDistributionBundle, the composer install/update commands and use in index[_dev].php
- [ ] Add requirement checker, but maybe ask Sensio if they can place the base of this in Symfony / SensioDistributionBundle / <??> rather then symfony-standard (avoid duplicating)
- [ ] Add unit test dist file for running src Bundle unit tests