Port DataDevice to the new inheritance approach

This was done mostly because I wanted to get rid of the Resource dependency in AbstractDataSource so I can make our xwl bridge more direct, but this also fixes up some issues with object lifespan present in the previous version and keeps all our clipboard code consistent.

Marking as WIP as I need to do IRL testing and one of the unit tests needs revising. I also didn't change the nested private classes, though arguably this is an unrelated task that could be done later.