Add emailing on server exceptions

Keymetrics VC's are coming. They no longer let you see reported
errors or notify you on their free tier which renders the service
useless for us.

This will emailing you using mandrill with a stack trace and
context of the error when it receives it

server/middlewares/keymetrics.js

@@ -4,5 +4,17 @@ export default function keymetrics() {
   if (process.env.NODE_ENV !== 'production') {
     return (err, req, res, next) => next(err);
   }
-  return pmx.expressErrorHandler();
+  return (err, req, res, next) => {
+    if (res.statusCode < 400) { res.statusCode = 500; }
+
+    err.url = req.url;
+    err.component = req.url;
+    err.action = req.method;
+    err.params = req.body;
+    err.session = req.session;
+    err.username = req.user ? req.user.username : 'anonymous';
+    err.userId = req.user ? req.user.id : 'anonymous';
+
+    return next(pmx.notify(err));
+  };
 }