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