Refactoring of healthsystem via HealthFacility class + HealthFacilityList object

[marghe-molaro]

All resource constraints and disruption to resource access are enforced at the facility level. This means that when processing the HSI_EVENT_QUEUE we are never in need of accessing health-system wide information on a particular resource* (which is how information on resource availability is currently stored), but rather require accessing all relevant information for a particular facility at once.

We therefore propose introducing a HealthFacility class that would assist us in defining all relevant characteristics for a facility. This would make:

• access to all relevant constraints in a facility more straightforward and potentially faster;
• feature development much more intuitive;
• data and logging structures in the healthsystem module much tidier (lists of capabilities, equipments, beds, HSIs delivered, squeeze factors etc would be superseded by a unique HealthFacilityList object which handles all this info internally) 

Relevant HealthSystem facility attributes:

• ID, Level, HR capabilities (including clinics), equipment, consumables
• (supporting current/near future feature development): type (e.g. Public/CHAM/Private), services_available (if considering variation in service provision), management (e.g. if considering effect of management on performance), catchment_area, ...

*This is only needed when rescaling available resources, which only occurs max once a year.