Cleanups Spring Data JPA example.

Various cleanups to the Spring Data JPA example, including:

* Move repositories into service package and make them package private
  thus only expose the service interfaces to clients.
* Merge HotelRepository and HotelSummaryRepository and make service
  implementations package protected.
* Introduce integration test base class to bootstrap the app as
  SpringAppliation.run would.
* Refactor central test case to rather use Spring MVC integration
  testing framework.
* Add integration tests for repositories to execute query methods.
Merge pull request #9 from olivergierke/master

# By Oliver Gierke
* pull9:
  Cleanups Spring Data JPA example.