DATAREST-227 - Broke up AbstractWebIntegrationTest and its subclasses.

Decouple the test machinery of this class from the barrage of common test cases used against the various data stores. This way, other test suites that use the same integration approach don't have to be a part of this class hierarchy. Also move utilities and assertion methods into separate utility classes to slim down the class hierarchy.

Original pull request: #149.
DATAREST-227 - Renamed WebTestUtils to TestMvcClient.

Renmaed WebTestUtils to TestMvcClient, added assertions to constructor and fixed formatting of JavaDoc.

Original pull request: #149.