Statistics - Canceled Reservations

[developeregrem]

A page must be created on which the number of rooms cancelled is graphically displayed. It also calculates how much money you may have lost/not received due to the cancellations (lost income). It should be noted that only days are taken where the room has not been allocated. Example: A period 5.1. - 9.1. was cancelled, but the room could be reassigned from 7.1. - 9.1. Consequently, two nights of the cancelled period may not be included in the calculation.

Assumes issue #15 is done.