Added link tag to favicon

Added the link tag to the favicon.ico

 This tells the browser to look for the favicon.ico in the same folder as index.html rather than the root of the server. 

If Kibana is found at 
http://example.com/kibana/index.html
it looks for the favicon.ico here
http://example.com/kibana/favicon.ico
instead of here:
http://example.com/favicon.ico

Apache access.log before(404)
10.0.0.15 - - [14/Aug/2014:15:52:39 -0600] "GET /favicon.ico HTTP/1.1" 404 499 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:29.0) Gecko/20100101 Firefox/29.0"
After: 
10.0.0.15 - - [14/Aug/2014:16:39:35 -0600] "GET /kibana_subfolder/favicon.ico HTTP/1.1" 200 1449 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:29.0) Gecko/20100101 Firefox/29.0"

Please consider this contribution public domain and free to be licensed as needed. :D