Configuring menu size

At first launch I was impressed: it was huge, took 2/3 of screen height.

I learned it's size depends on icon size setting of the panel later. But average users won't, and panel icons usually are bigger than menu icons, for reasons of space.

I see two approaches:
* use icon size of panel but reduced to 2/3 or 1/2
* configurable icon size/menu size
