Add copyright statements

[nmounet]

Copyright statements should be added at the beginning of all files, i.e. lines of the form:

# copyright ############################### #
# This file is part of the Xwakes Package.  #
# Copyright (c) CERN, 2024.                 #
# ######################################### #

A script exists (somewhere in Xsuite) to do that.

[lgiacome]

Closed by #27