Login functionality through Flask-Login and Flask-OpenID

Hello. This pull request adds features for login through openid. The changes that have been made are detailed in the commit messages. 

Three TODO have been added to views.py and marked TODO to indicate places that require changes after some developments in the future. 

The functionality was checked with a local sqlite database and google openid and worked as expected.

Do examine the request critically and let me know if any additional changes are to be made.