Update {epiparameter} usage

[joshwlambert]

This PR updates the {superspreading} package to use the latest function and class names from the {epiparameter} package (a suggested dependency of {superspreading}).

Since epiverse-trace/epiparameter#360 the <epidist> class was renamed <epiparameter> (see epiverse-trace/epiparameter#325). This came with functions that used the previous naming being removed, and epidist_db() became deprecated and replaced by epiparameter_db().

This PR replaces the use of epidist_db() with epiparameter_db(), renames get_epidist_params() to get_epiparameter_params() and replaces assertions that check the class from <epidist> to <epiparameter>. Error messages are updated, as is function documentation.

This is not a breaking change to {superspreading} as only internal functions are renamed or have arguments changed, and error messages are the only user-facing change. The vignettes are updated to call epiparameter_db().