final review of data flags has been done

The definition of data flags can be found in
chapter 5.2 of user guide
TOAR_UG_Vol03_Database_2021-04.docx

Data flags should be finally reviewed once again after documentation has been written.

Due to confusing description (and just for reasons of completeness), the old proposed flagging system has been deleted from this issue's description and put into a separate comment (...) -- this comment appears late "in history", but was actually the first description.