DatasetFilter: Create object for data set filter
In Novartis/subpat: Subpopulation and subgroups shiny modules

Create object for data set filter

DatasetFilter(
  dataset_name,
  variable = NULL,
  filterType = c("categorical", "date", "numeric"),
  catValues = NULL,
  minVal = NULL,
  maxVal = NULL,
  includeMissing = FALSE,
  onlyMissing = FALSE
)

`dataset_name`	data set name to filter on
`variable`	name of variable from 'dataset_name' that we are filtering on
`filterType`	One of "categorical", "date", or "numeric"
`catValues`	If categorical is selected for `filterType` should provide a vector of choices to select. A subject will match if `variable` is in `catValues`
`minVal`	the minimum value to match if `filterType` is "date" or "numeric". Selected values greater than or equal to `minVal`
`maxVal`	the maximum value to match if `filterType` is "date" or "numeric". Selected values less than or equal to `maxVal`
`includeMissing`	Boolean. Should we include missing values? Defaults to `FALSE`.
`onlyMissing`	Boolean. Should we only include subjects with missing values from `variable`? Defaults to `FALSE`. Need to provide the value filter. If "categorical" type is given, then catValues must be provided. If 'date' or 'numeric' is given, one or both of minVal or maxVal should be provided.