We are reverting commit e48b7f7e. I think I did not really appreciate
then that the number of days since 1950-1-1 is another date index. It
is clearer to use just one date index, which is in the dbf files. So,
in effect, we replace everywhere the old 0-based date index k by `k -
d_init`. Note that we no longer need argument `d_init` for procedure
`dispatch_snapshot` and we no longer need to write `d_init` to file
`node_id_param.json`. Note also that the value of every node index
changes by the amount `d_init * e_overestim`.

To search those names more easily.

Instead of referring to an external file.

Update dbf files with field date instead of `days_1950`.

We need this since `inst_eddies_Aviso.py` imports `inst_eddies` which
is in the binary directory.

Instead of copying files from the cmake repositoty.

When reading an eddy.

Rather than with Unix-specific chmod command. This requires CMake `3.20`.

Following convention for the source of `configure_file`. See Scott
2021 k1077, § 19.7.

Use a symbolic link instead of appending to `sys.path`. THe motivation
is that in the Python interpreter, the following statements failed
before the present commit:

```python
import sys
sys.path.append("/path/to/Detection_eddies/Inst_eddies/Analysis")
import plot_eddy_contours
```

`sys.path[0]` then does not contain
`/path/to/Detection_eddies/Inst_eddies/Analysis` so
`plot_eddy_contours` could not find `util_eddies`.

When there are more than 3 input files. We recover the convenience of
commit b34b85a8, with the underlying generality of commit d365e754.

So we get the function without executing the rest.

So we can call it from another script with a generated list of files.

Because we are going to extract the rest of the script below into a
function.

Check we find a max-speed contour when `e%radius4 >= 2` and
`e%speed_cont%ssh /= missing_ssh`. See test `Set_max_speed_degenerate`
for a case when we do not find one.

And it is then conveninent to choose it from the command line.

So read `grid_ml.txt` at the beginning of the script and not in
function `plot_grid_bb`, and pass `grid_nml` instead of `shpc_dir` to
function `plot_grid_bb`.

The script `plot_eddy_contours.py` was becoming too complicated.

If `n_dates` has been defined in the namelist then it is used by
`read_column` and, after the call to `read_column`, it is already the size
of `ishape_last`. It is clearer not to redefine it.

Use separate directories for modules of each target to circumvent
[Issue 22898](https://gitlab.kitware.com/cmake/cmake/-/issues/22898)
of CMake.

Write input in json file instead of preparing a separate input file.