Extend favicon to multiple sizes

HTML5 and iOS supports and expects favicon at multiple sizes. If we have a vector graphics (eps or svg file) for the logo, we can use it to generate all the required sizes by means of various online tools. Here's a commit from the Jamoma web site illustrating what's needed:

https://github.com/jamoma/JamomaWebSite/commit/02aded0687a4d057f264c458dd4a40917efd2f65
