Improved responsiveness

Still not perfect, but more functional than before (I think, anyway). I redid the relative widths of the columns and the blocks within the columns and also put the available widgets scroll on just the widget blocks (excluding the title "Available Widgets" above them).

This makes the "removing" overlay kind of a mess, though, and I can't recall if it's better or worse than before I started messing around in the CSS.

I also reordered the code a bit to make it clearer what I was working with, which makes the diff kind of obnoxious. Sorry about that.