new Flagger and Stuff

this is currently actively developed under https://git.ufz.de/rdm/saqc/

ChangeLog

• rm all old Flagger (Simple/Dmp/Positional/...)
• in docstrings: saqc.flagger.BaseFlagger becomes saqc.flagger.Flagger
• rm flagger from SaQC init (because its always the same, an initialized flagger object can still be passed via flags-paramter)
• moved all masking magic from core to register (may we should find a better name/place for this?)
• masking is now directly invoked on a call to a function (via @register decorator)
• rm force-support
• replaced all occurence of flagger.BAD/DOUBT/etc with plain BAD/DOUBT/etc., which live in saqc.common.py
• to_mask is now scalar and not listlike anymore and use > instead of == for comparison (see #160 (closed))
• we now pass cleared flags with each call to a saqc-function
• flagger.getFlags(field) -> flagger[field]
• flagger.setFlags(field, mask, flag) -> flagger[mask, field] = flag
• flagger.initFlags(data=data) -> initFlagsLike(data) a function in saqc.flagger.flags
• flagger.initFlags(flags=flags) -> Flagger(flags) flags is existing Flagger/Dataframe/DictOfSeries with flag values
• rm flagger.merge()
• rm flagger.slice()
• flag=SOME_EDAULT now is exposed to all relevant functions
• signatures in function are now identical with Saqc-class functions
• fuzzy tests only run on scheduled pipelines (if setup in Gitlab->CI/CD->Schedules (very easy))

Followup todo's (in new MR's)

• make every TODO in code an issue and add a reference to the issue in TODO text
• clean up core.py
• rewrite none-fuzzy pytests for masking
• provide flagging schemes / translations (eg. Dmp, Simple, Positional, etc.)