Change output to html4.

Changed document type to be compatible with html5 so don't generate
xhtml.  Still work to do to remove some xhtml in templates.

Author: rouilj

website/issues/config.ini

@@ -81,7 +81,7 @@ error_messages_to = user
 # var to 'xhtml' too so all auto-generated HTML is compliant.
 # Allowed values: html4, xhtml
 # Default: html4
-html_version = xhtml
+html_version = html4
 
 # Default timezone offset, applied when user's timezone is not set.
 # If pytz module is installed, value may be any valid