Added len() support to datalayer.ResultSet.
Fixed DataObject.get_key raising an error instead of returning None when object has no set key.
Fixed DataField subclasses causing errors on data object creation.
Fixed datalayer.SqliteDriver handling of IS and NOT operators.
Fixed datalayer.SqliteDriver handling of None values.
Added ElasticSearch support to datalayer
Merge branch 'unstable' into feature/elasticsearch
Merge branch 'unstable'