Resolve "Plotting CMIP6 data on unstructured grids with psyplot"

Closes #15 (closed)

notebooks/demo/use-case_advanced_summer_days_intake_xarray_cmip6.ipynb

 ``` python
-# Path to catalog descriptor on the DKRZ server
-col_url = "/pool/data/Catalogs/mistral-cmip6.json"
+# Path to master catalog on the DKRZ server
+col_url = "https://swift.dkrz.de/v1/dkrz_a44962e3ba914c309a7421573a6949a6/intake-esm/dkrz_data-pool_cloudcatalog.yaml"
+parent_col=intake.open_catalog(col_url)
+list(parent_col)
 
 # Open the catalog with the intake package and name it "col" as short for "collection"
-col = intake.open_esm_datastore(col_url)
+col=parent_col["dkrz_cmip6_disk_netcdf_fromcloud"]
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