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`.

Useless: there is a symlink to `util_eddies.py` in directory Overlap
since commit 56ca8ea3.

Assume that a slice is in a directory
"{shpc_dir}/{orientation}/Slice_{slice}" where shpc_dir can be any
name, orientation is "Anticyclones" or "Cyclones" and slice is an
integer. Do not read or create any longer a file "orientation.txt" in
the slice directory. Add procedure `get_slice_dir`. Add dummy
arguments cyclone and slice to procedure `shpc_open`. Add dummy
argument slice to procedure `shpc_create`.

Return tuple or scalar from function `node_to_date_eddy`, depending on
new argument `only_date`, instead of returning a dictionary. The
function is easier to use. Also, it saves a useless computation if we
are only interested in the date index. Returning a dictionary was more
justified before commit 43d2eff6, we we also returned the date.

Better to see a single label than several labels at the same position.

A node is no longer identified by date and eddy index.

There were only three files in `Overlap/Analysis`.

Rename triplet to collection, `shp_tr` to shpc, shpt to shpc in
comments, identifiers and file names.

We are reverting commit b926e1b7 because now there are two SHPC input
directories for visible eddies, two SHPC for interpolated eddies and
edgelists in differents directories for the two orientations. Handling
the command line arguments would be awkward.

Move functions `in_window` and `open_shpt` from
`plot_eddy_contours.py` to `util_detect_eddies.py` since these
functions are also used, or will also be used, elsewhere.

Required since commit 1eca0742.

This can happen with Matlab data, if a node present in the edge list
is absent in the shapefiles.

Print time measurements only when time option is
activated. Motivation: we need reproducibility for the automated test.

For the test of the script in `tests.json`. Normally, we would save to
pdf, but pdf format includes a date stamp. So pdf is not convenient
for testing. So we include the format value in argument save and we
save to png for the automated test.

Read only the graph containg specified node. The orientation of the
corresponding eddy must be specified on the command line.

Adapt the central longitude of the projection, depending on window or
position of chosen node. Else we can have arrows crossing the whole projection.

With window option, the script used to plot all components in the
subgraph containing the nodes in the window. So the components stopped
at nodes inside the window. Now we do better: we plot all the
components intersecting the window. These components may extend beyond
the window. This is in particular better if a component has a
connecting part outside of the window. In the old script, this
component would have been plotted as two components.

We achieve this by adding components intersecting the window in the
`component_list` attribute of the graph. And we modify the function
`plot_all_components`: it no longer calls
`nx.weakly_connected_components`: it just plots all the components in
`component_list`.

We only call `nx.weakly_connected_components` through the function
`assign_all_components` if the script is run without the window or
node options.