Add Signup menu entry, move index.html to signup.html.
Add LoginHelpers to handle login and loggedInUser SessionVar.

Adds
Signup is only available when not logged in, logs you in on success.

It also currently redirects you to /, which no longer exists.
Switch signup form to not be an AJAX form.
Add not-blank validations to email and password fields.
Add User.findUser.

We’ll be using this for login.
Add login form/page.
Fix id of login page main section.
Guard index from not-logged-in users.
Add index.html.
Add basic chat form.

Currently chats aren't displayed, an alert is just popped up when the
chat is received.