Tests for dui/register.

Can be run in a browser via:

http://localhost/node_modules/intern/client.html?config=dui/tests/infrastructure/default-conf
(adjusted depending on where dui is relative to your web root)
Destroyable & Widget-attr intern tests; not sure if IE10 classList is acceptable
Refactor Slider to use refreshRendering instead of _setXXXAttr.
fix newlines
Get infrastructure tests running in Sauce Labs.
Doc bower install of dependencies.
Also link to docs directory.
fix tabbing in Widget-attr.js
Handle style prop passed to constructor on Safari.
create enteredViewCallback() method
Get tabIndex working on Safari.
Only works as a const; you can't change it after inserting the element into the document.
fix when document.register() supported natively
Widget-lifecycle and handlebars tests added.
Note that running register and Widget-lifecycle tests together will fail,
needs proper teardown & register cleanup.

Fixes #50.
Workaround lack of Intern sandboxing.
See https://github.com/theintern/intern/issues/6.

Even if we made a dui/register.clear() method, we still couldn't use the same
widget name in different test files because the native document.register() call
throws an exception if you try to register the same name twice.

Therefore, our only option is to make widget names unique across all the test files.
Slider (and other future subclasses) should define refreshRendering().

FormWidget and FormValueWidget should advise it, because they are merely
tweaking the output.
update executable flag