modify the current queue to booking appointment

1. Current system issue queue number to the the walk in customer.
2. Modify the queue system with additional features:
a. allow to book 7 days ahead of appointment
b. allow to add, modify, delete the appointment
c. allow to select the service staffs (existing db)
d. allow to select the type of service
e. display the daily booking schedule, include booking time, customer id, service staff id etc
f. check no overlapping of service staffs booking
3. reports ..
4. work on current pos...