Bug from commit aab0e5c0.

This test is equivalent to the test `Extraction_eddies_periodic` since
commit a07ffd55.

We want to plot a box if `"UNIFORM_LON_LAT"` is not in `grid_nml`. Bug
from commit b3d7bd98.

If we read `expanded_traj.json` then we have to go through the traj
key since commit a7e65973.

So it does not overlap with tick labels.

So we can process the database in the Seanoe repository, produced by
an older version where `UNIFORM_LON_LAT` is absent.

Simpler.

So we can test the number of nodes in the graph before creating an
empty figure.

Since we now have the script `orientation.py` to create it.

Add argument `y_inline` to function `plot_velocity`. Because the `y`
tick labels may be at a bad position. We are going to use this
argument in a script to create `orientation.pdf` in
`Inst_eddies/Documentation_texfol/Graphiques`.

If arguments are missing, it is better to know it before entering the
namelists.

This can happen in particular with no argument date and an empty SHPC.

`plot_eddy_contours`, for example, should just be able to say it has
not found any eddy when the date is not found.

The bug comes from commit 06c451e2.

Add default values to arguments of function `plot_velocity`.

We need axes to add eddy contours.