OAuth login

Created the functionality to let the user use facebook to login.
Google oauth

Created the function to do google+ oauth authentication.
Small changes to oauth class

Bug fixes, not important.
Twitter

Commented out the twitter code, could not get it working.
Slight changes to OAuth

Added documentation and took out close browser.
Made changes to server

Client side, added all the new calls that can be made to the server.

Made the Database object a global variable instead of creating the
object in every function.

Added the functionality server side:

When password is saved in database, it gets encrypted.
When password(Password is encrypted) is retrieved, it gets decrypted.
If the user forgets his username and password, he can retrieve his
password, by giving his email address.
A OAuth user table.
Experience column to user table.
The leader board.
Merge branch 'OAuth-Login'