Format select widget doesn't work in Panels

Or, for that matter, any UI toolkit that might change the HTML ID of the format element. The problem is that it's expecting a particular HTML ID that might not be the case in the rendered HTML.

I've created a tiny little patch that gets around this by setting a custom data-* attribute to capture the HTML ID of the value textarea. We can then use this in the jQuery selector that grabs the format select widget for that textarea.