Add a script to make favicons

[tbekolay]

Right now all of our asset authoring is done in Inkscape. However, Inkscape can't create .ico icon files, so I believe we've been using an online favicon generator. It seems that we should be able to do this ourselves using a combination of Inkscape and Imagemagick. I would also suggest that the script that does this adjust the document properties such that there are no margins around the logo when it's converted to a favicon in order to maximize the small 32x32 space.