Replaced low-resolution favicon with high-resolution favicon

The old favicon was not in high resolution and upsampling it created ugly bitmap artifacts. New version contains resources for 16x16 and 32x32. I don't have the original PSD, but this is a near-perfect replication. If the source PSD with vector paths is available, we should use that one. If not I think this is acceptable.

Either way I think the discussion around higher resolution graphics on the website should start. I'm happy to share the original PSD with vector paths if a decision can be made where they and sources files like them should be stored in the repo.