DATAREST-409 - Port RepositoryInvoker API to Spring Data Commons.

Introduced SupportedHttpMethods abstraction to be able to test the exposure of HTTp methods based on a CrudMethods instance only. Moved ResourceType to the core module.
DATAREST-415 - Moved to PersistentPropertyAccessor API.

We now use the PersistentPropertyAccessor provided by the PersistentEntity to lookup property values to benefit from store-specific customizations. Code that relies on value conversion by using a ConversionService now explicitly uses a ConvertingPropertyAccessor.

Related tickets: DATACMNS-596.
DATAREST-416 - Switched to IdentifierAccessor API where needed.

We now use the newly introduced IdentifierAccessor API to make sure we benefit from store specific optimizations when looking up identifier values.

Added some user class lookups to make sure the projection and resource mapping lookup works if proxies types are handed around.