Add "hidden" concept for form fields

i.e. include hidden fields but don't show label or other dressing

tailbone/templates/forms2/deform.mako

@@ -20,11 +20,8 @@ ${h.csrf_token(request)}
     % elif field in dform:
         <% field = dform[field] %>
 
-    ##       % if field.requires_label:
+        % if form.field_visible(field.name):
             <div class="field-wrapper ${field.name} ${'error' if field.error else ''}">
-    ##             % for error in field.errors:
-    ##                 <div class="field-error">${error}</div>
-    ##             % endfor
               % if field.error:
                   <div class="field-error">
                     % for msg in field.error.messages():
@@ -61,9 +58,10 @@ ${h.csrf_token(request)}
                 % endif
             % endif
 
-    ##       % else:
-    ##           ${field.render()|n}
-    ##       % endif
+        % else:
+            ## hidden field
+            ${field.serialize()|n}
+        % endif
 
     % endif