basic cors support

I still need to add real CORS support with full OPTIONS support...
Merge branch 'develop' into feature/cors-suppport
Merge branch 'develop' into feature/cors-suppport

Conflicts:
	src/Graviton/CoreBundle/Tests/Controller/AppControllerTest.php
return CORS Allow-Method headers
Merge branch 'feature/cors-suppport' into develop

That it for now, I'll add more headers a soon as we have an auth strategy
in place that needs them.