Added Undo Feature

[AryanG01]

Undo Functionality

Undo Command (UndoCommand)

• Implemented a new command to revert the last deletion of bookings.
• When executed, the command adds previously deleted bookings back to the system.

Delete Command (DeleteCommand)

• Modified to keep track of the last deletions and store them for possible undo operations.
• Added the deleted bookings to a list for undo functionality.

ModelManager (ModelManager) - Implementation of Undo Mechanism

• Maintained a list (deletedBookings) to store deleted bookings.
• Implemented methods (addToDeletedBookings, undoDeletion) to add deleted bookings to the list and perform undo operations.