Fixes to make inheritance work for fetch requests and adding support for direct relationships.

This is the version of https://github.com/project-imas/encrypted-core-data/pull/19 that only supports direct relationships instead of arbitrarily deep relationships. EG:

This is supported:
WHERE reletedEntity.id = 10
But this is not supported:
WHERE reletedEntity.anotherRelatedEntity.id = 10

Note that from a speed perspective this is likely just as fast as pull/19, it's just that the super deep nested relationships that pull/19 also supports will probably slow things down. I haven't profiled it though so I really don't know, just assuming since every relationship adds an additional join clause.