Fix: map should redirect to current challenge (#15723)

* fix(routes): /map redirects to current challenge

* fix(map): Normalize server map building

Localize all server code dealing with the map

* refactor(server): Remove unused services

* feat(Nav): Show Map button when no panes

This gives user the ability to quickly return to their challenge using a
known feature

* fix(server.map): Add caching to nameIdMap

Add caching to nameIdMap on the server

* fix(services.map): Fix map service

Move map building utils to map util. Fix bad import. Normalize challenge
lookup

common/models/challenge.js

@@ -0,0 +1,12 @@
+import { Observable } from 'rx';
+
+export default function(Challenge) {
+  Challenge.on('dataSourceAttached', () => {
+    Challenge.findOne$ =
+      Observable.fromNodeCallback(Challenge.findOne, Challenge);
+    Challenge.findById$ =
+      Observable.fromNodeCallback(Challenge.findById, Challenge);
+    Challenge.find$ =
+      Observable.fromNodeCallback(Challenge.find, Challenge);
+  });
+}