A number of PG-file bugs fixed:
(1) Reading txt file with the same format as the format created by export (Save as txt file) is fixed. Note that
4 heading lines exist that should correspond to : Name, Unit, Id and pos.
(2) Calculating hourly mean values should now result in the correct time period for hourly values.
(3) Change of time period from original PG-file to a new created file is now working.