Make fragments for common form controls act natural

[CPColin]

The form-controls-fragments branch modifies productForm.html to use fragments, which makes that file much shorter and simpler. Unfortunately, this also makes that template much less natural, because Layout.js only processes the layout fragment. We should be able to expand the JavaScript functionality to process the new form controls fragment.

The Thymol library exists, but explicitly targets Thymeleaf 2.1, so it might not work for us.

[CPColin]

The form-controls-fragments branch has some work on this. It's weird! It might be dangerous, too, because it uses JavaScript's eval() functionality to make the fragments work right. But it does work, so that's nice.