Abstract carehomes_parameters parameters to controls

[RaphaelS1]

As discussed, we now have many parameters that take same default values and can be grouped together, cleaner abstraction into controls would allow separated assertions on parameters, re-use of same defaults, more manageable carehomes_parameters function.

e.g. Instead of parameters:

vaccine_progression_rate = NULL
vaccine_schedule = NULL
vaccine_index_dose2 = NULL
vaccine_catchup_fraction = 1

We have a function:

vaccine_control <- function(progression_rate = NULL, vaccine_schedule = NULL,
vaccine_index_dose_2 = NULL, vaccine_catchup_fraction = 1) {
 ...
}

Put all the vaccine parameter checks in there (the ones that don't require other params) and then in carehomes_parameters we make these one parameter: vaccine_parameters <- vaccine_control()

[RaphaelS1]

Once #278 and #277 are closed