Add extensive Testing Scheme to ABM-modell

[xsaschako]

Currently, there are rudimentary possibilities to test a person in the ABM, see #6. We want to extend this.

Especially we need:

— Different stages of testing
— Capacity of tests
— Focus on specific subgroups, e.g., kids, older, symptomatic, event goers

Finally, we need to discuss which scheme makes sense.