Moved prefs.txt to sqlite.
Some speed improvements.
Renamed pref fields using prefix 'pr_' to avoid clashes with reserverd words in SQL.
Improved variable check & speed
Revised and sped up backup function
Removed a last dependency on Master-list...xlsx file.

Added is.strdate function (for checking variables in fieldbook)
Added support to check date columns in fieldbooks. Date format: yyyy-mm-dd.
Ignoring temporary files
Added: addCountries & dialog
Correcting pre-selecting countries.