update bower.json for new dcl, refs #34
Add test case for tabIndex, refs #34.
It's only working when tabIndex is declared in a mixin, not when it's in the
 props passed directly to register(), so I left the other test case commented out.
improve test case for tabIndex, refs #34
Get tabIndex, disabled, and onchange working for Slider, and add several automated tests, plus some whitespace cleanup.
Fixes for 2.0 event handling.

1. There shouldn't be any widget methods like onClick() anymore, unless the widget is using it
   internally, but then it should be called _onClick() with an underscore.
2. Widgets already inherit methods like onclick and onchange from HTMLElement,
   but they should define functions like onfoo() for non-standard event names.
3. All listener functions (even onchange) get called with single argument: the Event object.
Fixes and test for parsing attributes during declarative instantiation:

1. Allow globals (ex: store="myStore") for Object attributes.
2. Fix functions attributes like funcProp="console.log(...)"; they were being ignored.
3. Disallow globals for functions, ex: onclick="myFunc", since that's inconsistent
   with how native DOMNodes work, where you need to do onclick="myFunc();"
reenable removeAttribute() call, but fix bug on IE
Additional declarative tests to test the removeAttribute code in Widget::mapAttributes
Get test_Slider.html working with IE10.  Workaround broken IE10 pageYOffset.
StoreMap fixes
fix some doc/comments/code following @wkeese comments
including removing the mappedKeys definition feature
make sure stateful properties are enumerable
remove test that is now useless, remove clone
some jshint & test cleanups
move back Invalidating to not necessarily be a Widget
inherit from Stateful
update CONTRIBUTING.md to be more inline with current project