Cancelling rides

FEATURE: Cancel rides from the user side.
Expected output : After booking a ride, before/after displaying the bill add an option to cancel the ride.

On cancellation, availability of driver should be changed, bill shouldn't be registered (make appropriate changes so it isn't seen in the admin section under view bills).

Optional: Add a feature of driver ratings. On cancellation, ask the user to select a reason for cancellation.
If it is the drivers fault, decrease the rating of the driver. (Let this feature be solely based on number of cancellations). If this is implemented, display ratings of all drivers while displaying availability during booking.

Potential bounty that can be earned:
Bounty Points (apply for all successful PR submissions): 60