Modified value of Qsl status that is printed in Qsl column of cards
to match the meanings of Qsl_Sent and Qsl_Rcvd statuses. Potential
values are now "Pse", "Tnx" and "". The determination of these
values is performed in DispQso class.
Added new tests class called DispQso to test all possible combinations
of Qsl_Sent and Qsl_Rcvd to ensure that the correct Qsl status is
determined.