Move this function from maintab.cpp to qthelper.cpp. Since the functionality was used in numerous places, use the helper function there as well. This removes a number of inconsistencies. For example, sometime setTimeSpec(Qt::UTC) was called, even though the QDateTime object was already created with that time spec. Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>