Added createReservation and incomplete updateReservation in new router

[Prakhar896]

Overview of changes:

• Added a new router confirmReservation.js
• Changed Reservation, FoodListing and Guest models for better junction table operation and to remove redundant keys
• createReservation endpoint in new router that is functional. Uses validateToken and has all data validation in place
• updateReservation endpoint is incomplete and under construction

Sensitive changes:

• Changes to model files including Reservation, FoodListing and Guest. Please drop tables before booting to ensure db synchronisation.
• Reservation table has new referenceNum key that is also included as a composite primary key along with listingID and guestID. This key is globally unique, enforced programmatically.