Flags

this is the followup of !217 (closed) and therefor should be merged after it. Moreover before integrating this in the real SaQC it should be rebased on develop before changing any the saqc-functions.

Dont get confused, we have here very few new code. infact the only new file in this MR is flags.py+ test, the other files-diffs are shown, because this sits on top of backtrack(!217 (closed)), where the BT-class is now called History.

Woohoo, now there is a extra Reviewer field :D