[TASK] Add our LICENSE notice to every v3 file

This is the notice we used before. It needs to be at the top of pretty much every single source code file we ship out.

# -------------------------------------------------------------------------------
# magpylib -- A Python 3 toolbox for working with magnetic fields.
# Copyright (C) Silicon Austria Labs, https://silicon-austria-labs.com/,
#               Michael Ortner <[e-mail]>
#
# This program is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option) any
# later version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
# PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
# details.
#
# You should have received a copy of the GNU Affero General Public License along
# with this program.  If not, see <https://www.gnu.org/licenses/>.
# The acceptance of the conditions of the GNU Affero General Public License are
# compulsory for the usage of the software.
#
# For contact information, reach out over at <[e-mail]> or our issues
# page at https://www.github.com/magpylib/magpylib/issues.
# -------------------------------------------------------------------------------
"""

[OrtnerMichael]

sw33t

[OrtnerMichael]

things are now with the SAL legal department