For clarity. Possible since commit 7d6308f6.

This is not really useful. If necessary, we can extract a component
with `extract_component_nx.py` or `extract_component.py`.

Move Python scripts to new sub-directory `Analysis`.

Move component extraction functionality to new script
`extract_component_nx.py`. For clarity.

`plot_traj.*` is the output of `plot_traj.py`. We should have renamed
the output file when we renamed the script in commit 328c6e3b.

Because we want to factorize what follows.

Edge list file is not necessarily in current directory since commit
c328203b.

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.