implemented google oauth

[Anirban780]

Let me state the changes I have made:-

1. I have made login page as index.html and main page as home.html so that user first authenticates using google
2. I have made necessary changes to add sign in button with google in login and signup page
3. I have removed the log in button from home page and added user profile, user name and log out button from google account data
4. For google client id, please create credentials and add the google client id in login(index.html) , home page(home.html) and signup.html
5. And, for normal sign in and sign up format, I have not made backend files to store user credential data and kept it untouched.
6. Now, user can log in using google account for simple authentication.

Let me know if I have to make other changes or improve the current above changes