Code style cleanups

Add keyword arguments. Sort arguments and models.
Move literals to their own module. Prepend handler_ to
signal handlers.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/metadata/views.py

@@ -69,7 +69,7 @@ class DocumentMetadataAddView(MultipleObjectFormActionView):
                     'Selected documents must be of the same type.'
                 ), request=request
             )
-            return HttpResponseRedirect(self.previous_url)
+            return HttpResponseRedirect(redirect_to=self.previous_url)
 
         return result