Key performance indicator: Case report source [5]

[MateStrysewske]

This is a first step towards implementing KPI (key performance indicator).

[MartinWahnschaffe]

See #904

• [ ] add a new dashboard called "KPI" to be seen by all national users. Extend button in the top right
• [ ] use existing statistics backend method (see #1348) to get case counts for field users (informants & officers, see UserRole.getInformantRoles, getOfficerRoles) and total case counts (= 100%)
• [ ] diagram shows proportion of cases created in the field by region over time (see https://github.com/hzi-braunschweig/SORMAS-Project/files/3546917/SORMASPerformanceIndicatorGZI_bsi_190816_gek.pdf figure 3)
• [ ] use same time grouping used for epi curve in surveillance dashboard
• [ ] add a disease filter (null uses sum of all cases).
• [ ] add a region filter (null shows all regions as lines)