add core-style. still lots of issues but is somewhat usable.

This still needs a lot of work; using it requires too much interop. Given the global nature of the element, though, I don't think a core-style-dart would really work. Ideally we could have data binding interop, which would probably let us set CoreStyle.g from a Dart object.
this had to be a JS script because otherwise it hits a timing issue.