[BUGFIX] Add missing support for belongsTo in DS.EmbeddedRecordsMixin

- active_model_serializer gem `has_one` setting allows embedding objects
- Add attrs options for serialize/deserialize using records or ids
- Add attrs options for not serializing relationships using serialize:no
-Add a hook called removeEmbeddedForeignKey for optional removal of foreign key reference from the embedded record
Merge pull request #1637 from pixelhandler/ams-has-one-embedded-belongs-to

[BUGFIX] DS.EmbeddedRecordsMixin support for belongsTo relationships