Captcha and design works.

Added captcha generation. As we're working without JS - there is no
possibility to reload image, only if user will reload whole web page.

Some design works - set monospace font for paste textarea (will
use system-defined default monospace font) and lowered font size
in paste views.

assets/paste.html

@@ -32,7 +32,7 @@
             </div>
         </div>
     </nav>
-    <section class="section">
+    <section class="section paste-data">
         {pastedata}
     </section>
 </body>