Added a ReferenceField widget
Added a ReferenceField widget

Also removed the unused ReadOnlyBool widget (as we now have a
properlyworking ReadOnly widget).

Patch by: Sverre Rabbelier

--HG--
extra : convert_revision : svn%3A32761e7d-7263-4528-b7be-7235b26367ec/trunk%401845

rhyolight/nupic.son,rhyolight/nupic.son,rhyolight/nupic.son