Listbox role support and other enhancements for deliteful/list/List

This updates the List widget with the following capabilities:

* Support for WIA-ARIA role listbox (fix https://github.com/ibm-js/deliteful/issues/56 and https://github.com/ibm-js/deliteful/issues/73)
* Support for new selectionMode "radio"
* No more default checkmarks on selected items (accessibility issues with VoiceOver when using checkmarks), addition of samples that demonstrates how to use your own (https://github.com/ibm-js/deliteful/issues/49 can be closed)

According to my accessibility tests, https://github.com/ibm-js/deliteful/issues/46 could also be closed.

By the way, I just started a search on my workspace files to migrate assert.equal to assert.strictEqual, and it appears that there are 495 occurrences of it in delite and deliteful tests.

I'm fixing it for List and StarRating tests, and opening a issues in delite and deliteful to have it fixed for the other tests.