Add option to view various sized qr codes on url page(Closes #20)

- pretty simple, just added a section to pick s,m,l code viewing
- used 'pre' to make it 'pre'tty. let me know if it's too much.

go/go/templates/link_box.html

@@ -9,6 +9,9 @@
   legend {
     font-size: inherit;
   }
+  pre {
+    font-family: inherit;
+  }
 </style>
 
 <div class="container">
@@ -64,6 +67,15 @@
         <i class="fa fa-linkedin-square fa-3x"></i>
       </a>
     {% endwith %}
+
+    {% with the_url|add:"?qr" as qr_url %}
+      <pre><strong>QR Downloads:</strong>
+        <a href="http://chart.googleapis.com/chart?cht=qr&chs=120x120&chl={{ qr_url }}">Small (120x120)</a>
+        <a href="http://chart.googleapis.com/chart?cht=qr&chs=230x230&chl={{ qr_url }}">Medium (230x230)</a>
+        <a href="http://chart.googleapis.com/chart?cht=qr&chs=350x350&chl={{ qr_url }}">Large (350x350)</a>
+        </pre>
+    {% endwith %}
+
   {% endwith %}
   </div>
 </div>