Different tags for different filter functions

[cdemulde]

Create a different tag for the different filter functions, so the user can always find out based on which filter algorithm a datapoint was dropped. Possibly plotting can be adjusted based on this as well.
This will require a lot of small code adjustment in a lot of functions.

[cdemulde]

See also Alferes et al, 2017, Validating data quality for water quality monitoring: Objective comparison of different data quality assessment approaches, Proceedings ICA2017