This commit also switches to a hardcoded version ("3.0") to the version
from Git (like the Go executables use). Because there are no tags for
this branch yet, this is just the Git commit hash.
The add-on code was copy-pasted from other addons and used the GPL v2
license, whereas by accident the LICENSE text file had the GNU "Affero" GPL
license v3 (instead of regular GPL v3).
This is now all streamlined, and all code is licensed as "GPL v3 or later".
Furthermore, the code comments just show a SPDX License Identifier
instead of an entire license block.
