menu applet: move recent clear button back to the bottom of the recent list.
It really looked out of place at the top, where I think you should immediately
see all your recent files, not a special button.

I'd like to consider some sort of dynamic clear button (or just a symbolic icon)
in the upper-right corner of the menu, that appears only when you're in the
recent category, and only if there are recent files to be cleared.