Gcef related fixes and features

See merge request !77

Bump numpy from 1.18.1 to 1.19.1

See merge request !63

Bump scikit-learn from 0.22.1 to 0.23.1

See merge request !72

Bump six from 1.14.0 to 1.15.0

See merge request !74

Bump pyarrow from 0.16.0 to 1.0.0

See merge request !67

it, matplotlib will choose one, according to the available libraries
on the system

Bumps [six](https://github.com/benjaminp/six) from 1.14.0 to 1.15.0.
- [Release notes](https://github.com/benjaminp/six/releases)
- [Changelog](https://github.com/benjaminp/six/blob/master/CHANGES)
- [Commits](https://github.com/benjaminp/six/compare/1.14.0...1.15.0)

Bumps [scikit-learn](https://github.com/scikit-learn/scikit-learn) from 0.22.1 to 0.23.1.
- [Release notes](https://github.com/scikit-learn/scikit-learn/releases)
- [Commits](https://github.com/scikit-learn/scikit-learn/compare/0.22.1...0.23.1)

Bumps [pyarrow](https://arrow.apache.org/) from 0.16.0 to 1.0.0.

Bumps [numpy](https://github.com/numpy/numpy) from 1.18.1 to 1.19.1.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/master/doc/HOWTO_RELEASE.rst.txt)
- [Commits](https://github.com/numpy/numpy/compare/v1.18.1...v1.19.1)

a implementation with a finally clause would be possible, but make the code look like spaghetti. :P

i removed the setup of the logging module from the core. It interferes
with the needs of the user of the lib (saqc). eg. Messages are double
printed or not at all.

>> It is strongly advised that you do not add any handlers other than
>> NullHandler to your library’s loggers. [...]
from https://docs.python.org/3/howto/logging.html

we might add a defalutLoggingSetup(log_level='INFO') function or similar in future,
to ease the setup the logging.

The tests wasn't included in the last merged merge-request !52 (masking b),
because it was a complete rewrite from scratch, because !45 was outdated.

Masking b

See merge request !52

Data that is flagger.BAD is masked by default.
One can pass a flag or a list-like to the param to_mask to control the behavior.
Pass an empty list to disable masking.
Nevertheless IFF the index changed the masked data is not restored.
Also flags are NOT restored IFF they considered _flagged_ before the func call, but not afterwards anymore.
Also any data that is set on masked locations is not overwritten by unmasking.