Update composer.json

sonata-project/notification-bundle is a requirement because the service "sonata.page.notification.create_snapshots" has a dependency on a service "sonata.notification.backend"
Updated german translations.
Merge pull request #188 from Lexance/patch-1

Updated german translations.
Merge pull request #187 from simonchrz/patch-1

Update composer.json
Merge branch 'sonata/master'

Conflicts:
	composer.json