Feature/force filtering

[cmbankester]

Added an observable called forceFilter that tells the datatable to filter the rows even if the current filter is undefined / "". The use case for this is for matching / filtering records on things other than the filter, e.g. on user-selected, pre-defined curricula.

For instance, I have this match function in an application:

class Row {
  ...
  match(filter) {
    return this.matches_component_role_filters() && (
      this.employee_id.toString().indexOf(filter) >= 0 ||
      this.name.indexOf(filter) >= 0
    );
  }
}

In the event that the table is filtered and there is no filter provided from the filter observable, the value passed to the match functions is an empty string.