Capturing of hidden variables

[JRPearson500]

Hidden variables are typically used in agent-based simulations. An example of such a variable would be the presence of an infection before the agent has started displaying any symptoms or has been diagnosed by a doctor.

Whilst the Alpha data model does not explicitly make use of them, they could be incorporated via the Patient kwargs variable,
which can be set in the config script.

If common hidden variables were identified, these could be added as Patient attributes, perhaps with some naming convention
(such as a prefix hidden_) to clearly indicate its scope. Adding hidden variables and acting on their values will require changes to the core codebase, but should not be too complex to implement (although this depends on their intended use).