Couple of fixes:
* Close empty extender when clicking in it.
* Saner size policy for Plasma::Meter. (the height should never be able to be smaller then svg's height because labels could otherwise overlap, actually, the whole current approach doesn't consider font size, I think we should think of a better approach for 4.3)
* Use the same spacer as used in the panel for extenders. I think we would want some svg themable shared spacer widget for 4.3, but at least this adds some consistency.