[WIP] Update composer.json for symfony2.3

I've tried to fix the issues I found, but at one point I didn't get any further.
https://github.com/symfony-cmf/RoutingExtraBundle/blob/0ef09de604700ae87265f533957908f171818631/Resources/config/cmf_routing.xml#L11

The `ConfigureableUrlMatcher`-class got removed and it is mentioned to use `UrlMatcher` instead. Don't know, how :( This is also the reason I dropped `2.1`-compatibility. Again don't know, if it is required for _every_ symfony-dependency.