Note that orientation = None is passed to `get_ishape_last` where it
becomes `self.def_orient`.

Move function `comp_ishape` to method of SHPC class.

`slice` is a built-in class of Python.

The global variable was used in the body of the function.

Rename `get_SHPC` to `get_slice` and `i_SHPC` to `i_slice`.

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`.

Use `e_overestim.txt` instead of `node_id_param.json`. Since commit
43d2eff6, we wrote only `e_overestim` to the JSon file. Simpler to
write the value alone in a text file.

Add script converting Graph-tool output to edgelist. So we can use
analysis scripts developed in Overlap on results of trajectory scripts.

Move tests on trajectories to new test file `Trajectories/tests.json`.