Add `shouldFallback` process env variable

So that it's clear to newcomers what things are not yet completed in scratch-www as we build it out.

README.md

@@ -30,8 +30,12 @@ Use `^C` to stop the node process `npm start` starts.
 | `API_HOST`    | `https://api.scratch.mit.edu`         | Hostname for API requests                      |
 | `NODE_ENV`    | `null`                                | If not `production`, app acts like development |
 | `PORT`        | `8333`                                | Port for devserver (http://localhost:XXXX)     |
+| `FALLBACK`    | `false`                               | Whether or not to fallback to `PROXY_HOST` for non-existent pages/reqeusts |
 | `PROXY_HOST`  | `https://scratch.mit.edu`             | Pass-through location for scratchr2            |
 
+#### Current issues with the development
+* Login does not work (*In the process of being fixed*)
+
 ### To Test
 ```bash
 npm test

server/index.js

@@ -79,10 +79,13 @@ if (!isProduction) {
         }
     }));
 
-    // Fall back to scratchr2 in development
-    // This proxy middleware must come last
-    var proxyHost = process.env.PROXY_HOST || 'https://scratch.mit.edu';
-    app.use('/', proxy(proxyHost));
+    var shouldFallback = (process.env.FALLBACK === 'true') || false;
+    if (shouldFallback) {
+        // Fall back to scratchr2 in development
+        // This proxy middleware must come last
+        var proxyHost = process.env.PROXY_HOST || 'https://scratch.mit.edu';
+        app.use('/', proxy(proxyHost));
+    }
 }
 
 // Start listening