Favicon

Add a favicon for Instiki.
Also, add an id for the svg path (which makes it reusable).

app/views/svg_logo.html.erb

@@ -1,5 +1,5 @@
 <span id="svg_logo"><svg version="1.1" width="100%" height="100%" viewBox='0 0 180 197' xmlns='http://www.w3.org/2000/svg'>
-      <path fill="#<%= @web ? @web.color : "393" %>" stroke-width='0.5' stroke='#000' d='
+      <path id="svg_logo_path" fill="#<%= @web ? @web.color : "393" %>" stroke-width='0.5' stroke='#000' d='
         M170,60c4,11-1,20-12,25c-9,4-25,3-20,15c5,5,15,0,24,1c11,1,21,11,14,21c-10,15-35,6-48-1c-5-3-27-23-32-10c-1,13,15,10,22,16
         c11,4,24,14,34,20c12,10,7,25-9,23c-11-1-22-9-30-16c-5-5-13-18-21-9c-2,6,2,11,5,14c9,9,22,14,22,31c-2,8-12,8-18,4c-4-3-9-8-11-13
         c-3-6-5-18-12-18c-14-1-5,28-18,30c-9,2-13-9-12-16c1-14,12-24,21-31c5-4,17-13,10-20c-9-10-19,12-23,16c-7,7-17,16-31,15