Adjust member category filter to allow parameters

Adjust member category filter to allow parameters

The member_category filter calls a function which has 3 possible
parameters, one of which allows any unassigned categories not to
show in the list. The filter itself did not allow these parameters,
causing empty categories to display whenever the filter is invoked.
The defaults for this filter are set to the same defaults that the
function has, meaning it should not impact sites already using it.