SIR implemented in ECS

Developer environment setup

Use nightly or change config file.

Use sccache.

Currently, the default toolchain should be nightly-gnu. There is an error with msvc.

TODO

Replications (reps) of scenario configuration is not implemented. These could be implemented in several ways.
1. Take the world out once it is fully formed, and then pass it to clones of App and run these. Then find a way to aggregate the results through something that summarises the reps.
2. After a world is done, next_repetition-method and then run the scenario once again. This next_repetition can do the following:
  
  rng: Increase the set seed by one, to get the next seed. recorders: Obviously these should be emptied, but they better retain the aggregated capacity. Disease compartments all set to zero.
  
  Re-run all startup systems, since these need to be generated again in order to ensure consistency throughout.