Fix for CustomButton click events. Fix for Widget layoutData/DockLayoutP...

The CustomButton wouldn't trigger clickHandlers that had been
registered. This would cause it and subclasses to not use the
clickHandlers. Fix the issue by triggering the proper event type. Left
in place the CustomEvent for back-compatability.

Widget has an issue when adding to a DockLayoutPanel. Related to
different scope rules b/t Java and Dart. Refactored layoutData var name
to fix the issue. For some reason when I did the fork, that change wasn't in there.

Looks like most of the change-lines are due to white-space differences. I used the Dart Editor formater prior to check-in.