Widget: remove support for data-dojo-id.

In modern browsers you can just say <my-node id=foo> and then reference window.foo.
Widget: Remove some outdated containerNode doc.
Note that containerNode still needs work/thought to make it work.
Widget: wemove code supporting _setFooAttr: "string" (instead of function).
Seems like we won't want to use it.
Widget: remove code to auto-generate id's.
Seems to no longer be necessary.
Widget: remove unused code, unneeded dojo dependencies.