Upgrade psymap version, add colormap and "free" attributes

[annefou]

• Upgrade psy-map version to the latest available (see https://anaconda.org/conda-forge/psy-maps)
• Add scientific and color-blind friendly cmcrameri colormaps (you can take https://github.com/galaxyecology/tools-ecology/blob/master/tools/data_manipulation/xarray/xarray_mapplot.xml as an example)
• psymap needs proper attributes (following CF-convention) but it is not always the case. Give the possibility to add attributes:
  - long_name
  - units