Basic validation, must have non-empty exchange sent and received.
Abstracted log view window widget behaviour into a base class. Turned
on auto resize to row height in log view windows and enabled
alternating colours. Convert empty fields to NULL when inserting new
log table rows to signify missing data. Trap insert row errors when
adding to contest log table so that logging can be held back if
constraints are not met. Re-factored log QSO processing to try insert
row into log table first and pop up a message box if constraints are
not met, this pops up the Log QSO window in case it was initiated by
an auto log event.
