DATAREST-329 - Improved RepositoryRestMvcConfiguration to not eagerly initialize beans.

The bean definition for annotatedHandlerBeanPostProcessor now is a static one so that it doesn't require the config class to be instantiated and populated, which caused the (too) eager initialization of all dependent beans.

Also we now leniently lookup all ResourceProcessor instances available in the context to prevent the lookup during config class preparation.

Ignore Neo4j tests now as they run into OutOfMemoryErrors.
DATAREST-330 - Exposed resources now support HEAD requests where reasonable.

The collection and item resources as well as the search and query method resources now answer HEAD requests according to the repository definition.
DATAREST-331 - Fixed invocation of processors for Resources subtypes in ResourceProcessorHandlerMethodReturnValueHandler.

ResourceProcessorHandlerMethodReturnValueHandler now also invokes ResourceProcessors that are typed to Resources even if the value returned by the controller is a sub-type of it.

Also added test cases for the invocation of processors for projections.
DATAREST-182 - Removed obsolete wirings from AbstractRepositoryRestController.

Removed the wirings for PlatformTransactionManager and ValidationExceptionHandler from AbstractRepositoryRestController. Removed the latter entirely as it doesn't seem to be used anywhere anyway.
DATAREST-332: Create @EnableRestRepositories to activate/configure SDR

* Provide alternative to @Import(RepositoryRestMvcConfiguration.class)
* Make it easier to alter baseUri (and other options in the future)
* Follow Spring convention of having @Enable annotation.