Refactor interface to plot_geography

[dnerini]

Addressing FutureWarning from 1.3.2 which concerns the interface to the plot_geography method.

In short:

• rename map to plot_map
• set plot_map as optional argument

Remaining open question:
Should we remove option to use the deprecated basemap module and leave cartopy as unique option?

[codecov]

Codecov Report

Merging #177 into master will increase coverage by 0.00%.
The diff coverage is 77.27%.

@@           Coverage Diff           @@
##           master     #177   +/-   ##
=======================================
  Coverage   74.39%   74.40%           
=======================================
  Files         110      110           
  Lines        8815     8802   -13     
=======================================
- Hits         6558     6549    -9     
+ Misses       2257     2253    -4     

Impacted Files	Coverage Δ
pysteps/visualization/animations.py	4.59% <ø> (+0.20%)	⬆️
pysteps/visualization/motionfields.py	72.65% <50.00%> (-1.23%)	⬇️
pysteps/visualization/precipfields.py	68.81% <66.66%> (-0.50%)	⬇️
pysteps/tests/test_plt_cartopy.py	84.21% <100.00%> (ø)
pysteps/tests/test_plt_motionfields.py	87.27% <100.00%> (ø)
pysteps/visualization/basemaps.py	49.42% <100.00%> (ø)

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[aperezhortal]

Nice work! For me, it looks ready to merge.

Remaining open question:
Should we remove option to use the deprecated basemap module and leave cartopy as unique option?

I'm in favor of removing basemap since last August they made their (likely) final release and it won't be supported anymore.

[pulkkins]

Remaining open question:
Should we remove option to use the deprecated basemap module and leave cartopy as unique option?

For me it looks like there is no reason to use basemap anymore. In 0.18.0b1, they finally added a feature that was missing from cartopy. Namely, lon-lat labeling with different projections (SciTools/cartopy#1117).

[dnerini]

All right, thanks @aperezhortal and @pulkkins. I'll merge this PR and open a new one for the deprecation of basemap.