Following update of NetCDF95.

Introducing `config_graph_nml`.

Following commit 3289c070.

Update `CMakeLists.txt` files for `test_get_dispatch_snap`.

Update `CMakeLists.txt` files to take into account commit 3289c070.

Remove dummy arguments nlon, nlat, copy of procedure `save_snapshot`,
use module variables instead.

Update `CMakeLists.txt` files to take into account commit 3289c070.

We can build some test sequential programs under Overlap.

Because we want to call `config_graph` in sequential program
`test_overlap`.

Remove unused procedure weight and corresponding unit test. weight is
not used since commit edb16459, after tag v0.20.

Change suffix because we are going to add preprocessor directives.

We are trying to define clearly the directories and what Fortran files
they should contain:

- `Inst_eddies`: May only contain program units which make up the
program `inst_eddies`. If a program unit does not go into
`inst_eddies`, it should not be here. Not all program units going into
`inst_eddies` must be here: some could be in directory Common.

- `Inst_eddies/Tests`: Main programs of unit tests for procedures in
directory `Inst_eddies`. Plus procedures used only in these unit tests.

- `Overlap`: May only contain program units which make up the program
`eddy_graph`. If a program unit does not go into `eddy_graph`, it
should not be here. Not all program units going into `eddy_graph` must
be here: some could be in directory Common.

- `Overlap/Tests`: Main programs of unit tests for procedures in
directory `Overlap`. Plus procedures used only in these unit tests.

- Common: Procedures that are used in both programs `inst_eddies` and
`eddy_graph`.

- Common/Tests: Main programs of unit tests for procedures in
directory `Common`. Plus procedures used only in these unit
tests. Plus procedures used in unit tests of both `Inst_eddies` and
`Overlap` directories but not used in either program `inst_eddies` nor
`eddy_graph`.

Remove dummy arguments nlon, nlat, copy of procedure `recv_snapshot`,
use module variables instead.

Remove dummy argument `max_delta` of procedure `dispatch_snapshot`,
use module variable instead.

Remove dummy arguments nlon, nlat, corner, step of procedure
`read_snapshot`, use module variables instead. Note that we keep copy
as a dummy argument instead of using the variable of module
`config_graph_m`, because we want the procedure `read_snapshot` to be
usable outside of the `eddy_graph` program.

Remove dummy arguments nlon, nlat, periodic, `dist_lim` of
procedure `overlap`, use module variables instead.

Remove dummy arguments nlon, nlat, corner, step, copy, `max_delta` of
procedure `get_snapshot`, use module variables instead.

Add `config_graph.f90`and `read_grid.F90` to lists of source files.

Which read namelists. Motivations: diminish the number of arguments of
procedure overlap; lighten the main program unit. We conditionally
compile MPI calls in `read_grid` because we want to use variables of
module`read_grid_m` in procedure `read_snapshot`, and `read_snapshot`
is called from sequential program `test_nearby_extr`.