Changes to anchored_artists.AnchoredSizeBar

Hey,

I've done some changes to anchored_artists.AnchoredSizeBar so it can be used to make scale bars as shown in for example: http://www.semiconductor-today.com/news_items/2012/MAR/12028UCLfig1.gif . 

Currently it is not possible to change the color of the label, because I didn't figure out how to change this in a TextArea.