User can mark a Patient as having NKDA

[francisli]

This was commonly observed during the latest distribution day.

NKDA = No Known Drug Allergies

Currently, an empty Allergies field could mean two things- the Patient has no allergies, or the allergies haven't been recorded yet.

NKDA is an example of a "pertinent negative," where the confirmation of the absence of something is important to highlight.

We should consider how we can model and record NKDA for a Patient.