Run tests using Intern 2.1 rather than 1.7.
iOS though not working yet, temporarily disabled.
Also switching to FF 31 and Chrome 36.
Makes delite/css layersMap reference the relative mid of the layer instead of the complete path.
fix API doc for startup()
Prefer attachedCallback() to startup().
Also, make createdCallback() and attachedCallback() automatically chain.
Removes chaining of startup() though, since subclasses generally shouldn't
extend it anyway.

Fixes #287, refs #283, refs #257.
Remove code from emit() to squelch events emitted before startup() call.
Fixes #288.
Remove _onKeyDown() extension point from DialogUnderlay.
User code can just call DialogUnderlay#on("keydown", ...), although in the case of Dialog
it seems easier to just listen for keydown events on <body> or <html> instead.

Also remove dcl.before() advice from destroy() method, since that method
is automatically chained.

Refs #281.
Remove underscore from names of protected properties:

* CustomElement: _created, _attached, _parseAttr --> parseAttribute, _parseFunctionAttr --> parseFunctionAttribute
* HasDropDown: _buttonNode, _arrowWrapperNode, _popupStateNode, _aroundNode
* KeyNav: _onLeftArrow, _onRightArrow, _onUpArrow, _onDownArrow, _getNext
* Widget: _started
Use eventNameHandler or _eventNameHandler for event handlers.
Fixes #281.

Note that _onFocus/_onBlur/onFocus/onBlur is tracked separately as #214.
remove vestigial code from when scroll bar was on popup wrapper, refs #266.