remove duplicate code in notebooks, `analysis/`

The Jupyter notebooks were updated to run correctly in previous commits, but they often used functions in the analysis/ folder which weren't used in the main library, and these weren't inspected. So we have two slightly different ways of e.g. obtaining CM2.6 ocean velocity data.

Also, a GlobalPlotter class defined in analysis/ is duplicated in some of the notebooks, with some changes (e.g. to keys used for the input dataset). At a glance these should be mergeable into a single instance.

[ ] replace get_patch, get_whole_data with calls to lib.data functions
[ ] have just one GlobalPlotter class

m2lines / gz21_ocean_momentum

remove duplicate code in notebooks, `analysis/` #111