Issue 133: Adds enum support as string fields during reads. Note that
before the patch the enum fields are already described as strings in the
metadata.
This commit fixes the following issues:
85	Provide support for @Embeddable/@Embedded attributes for non-key
types.
219	$expand broke in version 0.7 with JPAProducer 

The $expand feature worked in version 0.6 in a subomtimal fashion, not
eager loading (FETCH JOIN) the expanded properties but issuing n+1
queries. This fix commands JPA to eager load what is necessary as well.