Completed login function + chat page + minor changes

-Created log-in form with username and password in index.html. Also added a link to the sign up form
-Restructed app so that the login page is the main page.
-On submit of login button, an ajax request is made to the chat server and returns an API tolken key, which we use to make a get request for all the chat messages
-For the handlebar templates, created functions (display_*page*) that will clear content div and render the html for the specified page.
-Created a handlebar template for the Chat messages which gets rendered after succesful login
-Tested and passed run-through of signup, login functions + chat messages display
-Minor changes to class names. Note: username and password fields changed from id to class so that other templates can use it.