Tidying up _daily_capabilities/capabilities_today in HealthSystem #1618
Description
Currently, in the HealthSystem, the daily HR capabilities available are:
- Initialised via _daily_capabilities
- Accessed via the capabilities_today property, which multiplies the _daily_capabilities by the capabilities_coefficient every time it is accessed.
Originally, the capabilities_coefficient was supposed to represent some productivity scaler, which can be initialised through the module parameter. Currently, however, this capabilities_coefficient is only responsible for rescaling assumed capabilities by the simulated to real 2010 population size ratio. Given that this could/should be done once when the simulation is initialised, and that the discussion of HCW productivity has moved quite significantly from a single coefficient since this was first implemented, suggest merging _daily_capabilities and capabilities_today to avoid confusion.