[Dx4win] Feature request - Add QSO Date Filter "Less Equal" option to preferences

[Andreas Junge, N6NU]

One example is that I want to clear "QSL Date" fields that are older than
one year by filtering QSO with "Less or Equal" "12-15-2007" in the "QSL
Date"

The "Range" option does not appear to work on QSL date or the QSO. There is
no prompt. I could have used that one instead. 

73, Andreas, N6NU