Overlay serialization is broken

Overlays currently can be serialized and restored via a writeExternal() and readExternal() approach. However this approach requires that the serialized object has a no arg constructor. Currently the Data constructors all require at least 1 argument to the constructor. Until recently we were passing null as an argument safely. But with recent changes to the data type hierarchy this fake no arg approach fails and the test code in TestBinaryMaskOverlay began failing. I have commented out this test for now as we are not sure how we want to handle serialization going forward. We should figure out how we will support serialization of overlays and restore the commented out test,

Migrated-From: http://trac.imagej.net/ticket/1991

Start with the commented-out TestBinaryMaskOverlay test and trace the writeExternal() and readExternal() paths for overlays. Review the Data constructors and recent data type hierarchy changes to determine the supported serialization approach. Done means overlay serialization and restoration work without the current no-argument-constructor failure and the test is restored.

Written by the indexing model from the issue text.