Payment Prototype implementation

[Keeran10]

This is a sub-task of issue #5.

• Create a Payment Page for credit card payments.
• Return a confirmation message upon successful transaction.

Patients should be able to access the payment page through the checkout function from their appointment cart.

Project Description: You are not required to build the payment module, however you need a stub (prototype) that simulates the behavior of the payment.

[Keeran10]

Completed in pull request #50.