Separate grid- and projection- related properties in Domain.

Lint with pylint, but keep the flake8 pylint plugin inactive for the
time being. Some more tunning is still needed.

With a somewhat basic config/plugin usage for flake8 at the moment.

Update .pre-commit-config.yaml and .gitlab-ci.yml to use these new
configs.

Via config.general.obsoul_export_params

default=["pressure", "temperature", "humidity", "sum_rain_1"]

Move thinning_grid_coarse_factor config option from the
"commands.select" config section to the "domain" section.

Also, change scheme to choose resolution of shown grids (if any).

And make other minor cosmetic changes to them.

Plotly does not seem to take the used map projection into account to
interpolate between start and end (lon, lat) coords. Doing the
interpolation manually now.

Also format hover text properly and give back clickmode="event+select"
to cluster plot.

From plots.py. They are no longer needed.

And, in the process, use Domain's plot engine to produce scattergeo
plots.

And put it into new function make_simple_scatter_geo.

Further helps to distinguish clusters, as the number of colours is
limited.

For the cases when the refining procedure ends up removing all elements
of one or more clusters.

Also, made minor chnages to defaults so that test_clustering.py and
app.py produce the same results by default.

The colours of the poins corresponding to obs removed from the clusters
after running the post-clustering refining now match the colours of the
originating cluster. This makes it easier to identify such obs visually
in relation to their parent clusters.

The symbol is not the same used for the obs removed by the clustering
itself, as the colours lift the ambiguity.

Remove rejected/unclustered observation entries from the calculation of
the Silhouette score.

Minor change to plotting order so that accepted obs will be
plotted on top of the rejected ones.

Other minor changes.