Ensure that '_reference' key is used to store the reference
Added sensible defaults for keyForPolymorphicId and keyForPolymorphicType
Merge pull request #965 from ssured/master

Add sensible defaults for polymorphic keys
Merge pull request #964 from sandstrom/model-reference

Ensure that '_reference' key is used to store the reference
per type commit

group by adapter for type and then commit