Rendering/font size

Fonts have to be reinstalled in order to have a great font-size experience.
Run `CSSFontFormatter uninstallFonts` once - reinstallation should be triggered automatically on the next use of fonts.

Closes #99 
Seems to me like a questionable magic number: Why 2 and not 1/3/4?
I would suggest to ask Eric whether he wants this 'hack' (that kind of ignores the values Squeak provides) or not.