Example data:

2016-12-21 09:27:53;629
2016-12-21 09:28:53;642
2016-12-21 09:29:53;656
...

see https://bugs.kde.org/show_bug.cgi?id=374871

Tasks:

• Support Datetime when importing data - DONE
• Selected format for datatime import - TODO
• Preview in import dialog - TODO
• import into spreadsheet/matrix (?)
• plot data in datetime format : needs additional tick label format?

Ideas:

• Support also different numeric formats (see AbstractColumn.h)