RouteCollection no longer requires a ServiceLocator

Hi there,

@ocramius requested that Dash be added to [tyler-sommer/php-router-benchmark](https://github.com/tyler-sommer/php-router-benchmark/pull/5) and I've started working on that. 

However, to create a RouteCollection I needed a ServiceLocator. This PR makes the ServiceLocator optional for creating a RouteCollection.

I have a strong feeling that this is not actually what I should be doing, any help?