Remove attribute-style accesses to (Geo)DataFrames columns and xarray Datasets variables and attributes within tutorials

[spjuhel]

See also #939 for the codebase counterpart.

Changes proposed in this PR:

• Removal of attribute style-accesses to columns of pandas DataFrames, GeoDataFrames, and variables and attributes of xarray DataSets and DataArray within the documentation

This PR fixes SCRUM userstory 100: Avoid attribute-style access to DataFrame columns (https://tree.taiga.io/project/emanuel-schmid-climada/us/100).

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• Documentation updated
• Tests updated
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[luseverin]

Hey! Unfortunately I cannot open none of the modified tutorial files, as the notebooks seem to be broken (see the following error message, here for util_calibrate):
Expected ',' or ']' after array element in JSON at position 133145 (line 1692 column 57)
Apparently you removed one ',' or ']' when you modified the notebooks? You might want to check that out.

[spjuhel]

Woups, problems with the types of quotes used. Should be fixed now, sorry about that.

[luseverin]

I looked at your changes, it looks good now. There is still one typo to be fixed though.

Otherwise, I think I spotted a couple missed instances of attribute-style accesses:
In climada_hazard_TropCyclone.ipynb:
1753: "print('Daily max sustained wind:', tc_syn.max_sustained_wind.groupby('time.day').max())"
and in climada_util_calibrate.ipynb:
1042: "emdat_subset = emdat[(emdat.cal_region2 == \"NA1\") & (emdat.year >= 2010)]\n",

This aside, it looks all good, well done!