Completion century controlled by parameters

Currently the njx input controls don’t
support any parms to control the completion of a 6-digit date input with the
century. In the case of a 6-digit date input, the century is set to 2000, if
the year is in the period 00-49. If the year is in the period 50-99, century is
set to 1900.

To ensure compatibility between NAT (e.g.
MOVE EDITED) and NJX, NJX should also support a parm similar to NATPARM YSLW to
interpret the century of a 6-digit date input.