Tests: Moved mock objects 'expects()' calls inline to improve readability

Follow-up to [PR #99](https://github.com/symfony-cmf/RoutingBundle/pull/99) - see the comments there after it was merged.

Refactored unit tests to improve readability. I've removed the `BaseTestCase` class, created plain mocks in each test class' `setUp()` method and then configured them individually for each test.