popup.js: require dui/themes/load!common to get duiPopup class
Remove _AttachMixin, _TemplatedMixin, and _WidgetsInTemplateMixin.
They are essentially replaced by the handlebars plugin.
remove deprecated code etc. from helpers.js
Fix _Widget-attr test to work w/direct accessors.

Removed tests for automatic mapping of attributes, since that's no longer supported.   Also
removed tests for features that are covered by the tests for Stateful, and moved a few tests
to tests/Stateful.js

Finally, stopped using _TemplatedMixin in the tests since I'm going to remove it.
Stateful: fix comment
get _HasDropDown working again after ES5 accessors check in
popup test: removing _TemplatedMixin dependency
more fixes to _HasDropDown, test then squash
Use register() for declaring widgets and declare() for base classes.
Updated register() to search inherited properties too for shorthand notations
like _setFooAttr: "focusNode".