refactor graph generation to use bitarray instead of lightgraphs, much faster

CovidAlertVaccinationModel/src/CovidAlertVaccinationModel.jl

CovidAlertVaccinationModel/src/graphs.jl

CovidAlertVaccinationModel/src/mixing_distributions.jl

CovidAlertVaccinationModel/src/model.jl

CovidAlertVaccinationModel/test/runtests.jl

IntervalsModel/plots/hh.pdf

IntervalsModel/plots/rest.pdf

IntervalsModel/plots/ws.pdf

IntervalsModel/simulation_data/hh.dat

IntervalsModel/simulation_data/ws.dat

IntervalsModel/src/IntervalsModel.jl

IntervalsModel/src/hh_durations_model.jl

IntervalsModel/src/ws_durations_model.jl