TicketMonster - Data grid-based reservation system

1. Use a data grid to hold reservations

2. Introduce a 'hold' reservation state: the system will pre-allocate seats during the reservation process. It should be possible for users to add seats to the cart and confirm or cancel the reservation. Held seats can either be promoted to 'Sold' (upon a successful booking) or freed up (upon cancellation)

3. Demo clustering with data grid