VikBooking 1.18.21

Core reservations model improvements.
Updated task manager hook signature upon scheduling booking confirmation tasks.
Various improvements to the PMS reports framework.
New configuration setting "booking details link expiration days".
Front-end booking details page door access codes "not yet available" message.
Booking device passcodes hook for manipulating generated door codes.
New booking details SID default format with dedicated hook for adopting a custom format.
New transient tokens model.
New configuration setting for keeping certain guests related media files above the web-root directory.
SVG and images sanitising techniques.
Various CSRF and capability checks added.
Various fixes and value escapings applied.