Gravatar image fixes when gravatar unavailable

Created by: karlhungus

-Alt text to image was set to hash, which would make the page display hashes if the image/gravatar wasn't available, set the alt text to '', and made the main tool bar image follow the same or similar constraints as the other images (.avatar, .s26)

Conflicts: app/assets/stylesheets/themes/ui_bb.scss app/views/snippets/_snippet.html.haml