List priority epidemiological parameters for the database

[joshwlambert]

Please also add explanation for why the epidemiological parameters are a priority and the use case that it applies to (including R packages). E.g. an Ebola onset-to-death distribution is required for calculating the unbiased case-fatality risk using the R package {cfr}.

[pratikunterwegs]

Some I can think of from models currently included in {epidemics}; some might already be included in {epiparameter}.

1. Incubation period; this is used to calculate the transition from exposed to infection ($\sigma$);
2. Onset to hospitalisation; for the hospitalisation rate in the Vacamole model $\eta$;
3. Hospitalisation to outcome (recovery/death);

Would I be right in thinking that onset-to-death distributions could be generalised to any outcome? Or would onset-to-recovery (for the recovery rate) be expected to be much different?