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 function `partition_graph_date` from script `report_graph.py` to
script `edgelist_to_Graphviz.py`. `partition_graph_date` is no longer
used in `report_graph.py`.

These files will usually be created in the same directory.

Correct the test to know whether we can use part of the properties
already calculated for the beginning of the segment. When `len_seg ==
2 * n_days_avg`, `g.vp.inst_eddies[n][-n_days_avg:] =
g.vp.inst_eddies[n][n_days_avg:]` so
`g.vp.inst_eddies[n][:n_days_avg]` and
`g.vp.inst_eddies[n][-n_days_avg:]` are disjoint. The bug comes from
commit bdd0ce41.

So that corresponding dates are in a possible
order. `edgelist_Isic_2.csv` still has the same edges than
`edgelist_Isic_1.csv` in a different order. Note that we also have to
change `e_overestim`.

Following the  move of `extract_component.py`.

Move script `extract_component.py` from directory Trajectories to
directory Overlap. It does not deal with trajectories and it does not
need the input graph to be a graph a segments.

This is useful to find the shortest path between the beginning and the
end of a trajectory, or to create a histogram of the number of
trajectories per component.

Bug fix: correct sign of variation of Rossby number and radius. We
have to be consistent with the computation of `delta_ro_mean` and
`delta_r_mean`. `delta_ro_mean` and `delta_r_mean` were computed by
subtracting origin from tail.

It does not make sense here to assume an ellipsoid: the computation of
the distance with $\cos \phi \delta \lambda$ and $\delta \phi$ is a
rougher approximation than treating the Earth as a sphere.

We avoid multiple conversions to rad of the same value, in the loop on
edges, since a segment can be head or tail of several edges.