provides a more helpful error msg when a new feature is created with an existing name

lib/routes/feature.js

@@ -20,7 +20,7 @@ const handleErrors = (req, res, error) => {
         case NameExistsError:
             return res
                 .status(403)
-                .json([{ msg: `A feature named '${req.body.name}' already exists.` }])
+                .json([{ msg: 'A feature with this name already exists. Try re-activating it from the archive.' }])
                 .end();
         case ValidationError:
             return res