Extend session with "remember me"

[psvenk]

Closes #246. Instead of just storing the username in client-side storage and populating it on the login page, keep the user logged in for up to 30 days if they select "remember me".

Please note that I have not yet tested this code.

[psvenk]

I just now tested this code with the following change applied so that I would not need to wait for 8 hours:

diff --git a/serve.js b/serve.js
index b0df969..b9f1415 100644
--- a/serve.js
+++ b/serve.js
@@ -108,10 +108,10 @@ app.use(express.static(__dirname + '/public'));
 app.use(bodyParser.urlencoded({ extended: true })); // Allows form submission
 app.use(bodyParser.json()); // json parser
 app.use(session({
-    // Sessions expire every 8 hours
-    cookie: { maxAge: 8 * 60 * 60 * 1000 },
-    // Check for expired sessions once per hour
-    store: new MemoryStore({ checkPeriod: 60 * 60 * 1000 }),
+    // Sessions expire every minute
+    cookie: { maxAge: 60 * 1000 },
+    // Check for expired sessions once per second
+    store: new MemoryStore({ checkPeriod: 1000 }),
     resave: false,
     saveUninitialized: false,
     secret: crypto.randomBytes(64).toString('hex'),

Without "remember me", my sessions expired after a minute; with "remember me", they were still valid after more than two minutes. I would like someone else to do some testing if possible before we merge this.