Add additional handlers

Hi,

Here is a pull-request to add additional handlers :
 - ezobjectrelation : this datatype doesn't support information collection, but this handler can be useful to use csv parser for general csv exports (like general content objects)
 - owenhancedselection : this datatype is an enhancement of ezselection ( see https://github.com/Open-Wide/OWEnhancedSelection for details )

Cheers,
Simon Boyer
This line should say 'File containing the ezobjectrelationhandler class.' instead