Allow visit deletions

With the arrival of note pre-fill, Instinctive Notes now support visit deletion.

This is because if a visit was created from an appointment which then was cancelled then the visit should be removed.

Alongside removing the visit from the Instinctive Notes App, visit deletion will also remove the visit from display across Instinctive Notes Web, from any visit exports and also process correctly for our external integrations with Cliniko and Nookal.