Created/added SVG Groovy logo

This makes the main Groovy logo resolution independent. The new logo looks much crisper on retina screens like the iPad Air. There is also a fallback for IE 8 and below to use the PNG version of the logo.

Before: https://dl.dropboxusercontent.com/u/11285872/groovy-logo-before.png
After: https://dl.dropboxusercontent.com/u/11285872/groovy-logo-after.png