Compute `i_slice` in `comp_ishape` if `i_slice` is None. Add default
value of None for dummy argument `i_slice`.

Move dummy argument `i_slice` of function `comp_ishape` to last
position. Because we are going to add a default value.

For `Test_compare` version > 0.4.

Move functions `node_to_date_eddy` and `date_eddy_to_node` from script
`report_graph.py` to script `util_eddies.py`. `util_eddies.py`
contains more basic functions, it only imports
shapefile. `report_graph.py` imports networkx. It was not convenient
nor meaningful to require networkx for scripts that use
`node_to_date_eddy` or `date_eddy_to_node`.

This was polluting standard output. So we have to add the shapefile
path when it is not found.

OSError is more specific than SystemExit. It is better to have a more
specific exception when we want to catch it.

Invert order of dummy arguments orientation and layer of method
`get_reader`. Take the same order than in the path. `orientation` was at
the end because, at first, in commit d858fb72, it was an optional
argument.

Check that `SHPC_dir` exists at initialization of instance of class
SHPC. Before this commit, if `SHPC_dir` did not exist, there was an
error trying to create `n_slices.txt`, which was less clear.

Remove unused procedures and programs `inside_4`,
`max_speed_contour_ssh`, `test_inside_4`,
`test_max_speed_contour_ssh`. Unused since commit 99e2e1b1.

Remove component radius4 of derived type eddy and field radius4 of
`outermost_contour.dbf`. They are not used any longer.

Because `test_set_all_outerm` is now essentially the same as
`inst_eddies`. Replace `test_set_all_outerm` by `inst_eddies` in
tests.

Move the second test on `self._ishape_last[i_slice][orientation]`
inside the first test. Avoid the double test on
`self._ishape_last[i_slice][orientation]` when
`self._ishape_last[i_slice][orientation]` is not None on entry of the
function. If `self._ishape_last[i_slice][orientation]` is not None on
entry of the function then, necessarily, the assertion on
`self._ishape_last[i_slice][orientation].size` and the definition of
`self._e_max[i_slice][orientation]` have already been done because
`self._ishape_last[i_slice][orientation]` and
`self._e_max[i_slice][orientation]` are only defined from the function
get_ishape_last.

In function `comp_ishape`, return None instead of crashing if eddy
index is greater than max. This allows the script
`write_date_range.py` to work with an input SHPC containing a date
without eddies.

In function `comp_ishape`, check that `eddy_index` is in the right
range.

Preparation for a check in `comp_ishape`.

Dictionary instead of list, following update of `test_compare.py`.