Port marshal_datasets() to new experimenter_id structure

Added tests for an experimenter_id of None, refactored
marshal_datasets() into new structure and added proper sorting
semantics.
Port marshal_plates() to new experimenter_id structure

Added tests for an experimenter_id of None, refactored
marshal_plates() into new structure and added proper sorting
semantics.
Add tests for an experimenter_id of None
Remove soon to be unused methods and associated test cases
Remove debugging
Ensure we are only loading orphans in marshal_datasets()
Ensure we are only loading orphans in marshal_plates()
Use projection for all tree view data