Read and write the settings only from the preferences dialog.
Remove all the copies of some settings which were stored in nearly every
dialog class individually.
Simplify the settings dialog code by removing all those not really
needed slots.
Rewrite the dialog to export tables as CSV file using Qt Designer.
Move the entire export functionality to this dialog instead of
generating the file in the main window.
Add some options for the user to change the layout of the CSV file.