Reorder search filters so the more common ones are nearer the top of the menu, without breaking up the obvious groupings that aid scanning.

We might put in additional space between groups later to aid chunking. Or that problem might be obliterated by an improved query language that doesn't require such attention to the types of identifiers.
Improve the look of the Filters menu (and, incidentally, the Switch Tree menu).

* Remove borders between menu items, reducing noise.
* Condense menus, which gives the Filters menu a chance at fitting in the viewport without scrolling.
* Lighten menu text so the huge mass of bold labels isn't so overwhelming.
* Give the tree descriptions a class. We'll come back later to columnize the tree menu.