Adjust the loading of BAT from a wheel file in such a way that all
submodules are loaded in one go. This ensures that they're still
isolated from the rest of Blender (so other add-ons won't find our BAT),
but not from each other (so that there is only one copy of each
submodule).
In practice, this solves an issue where calling
`blender_asset_tracer.blendfile.set_strict_pointer_mode(False)` had no
effect. This was caused by each loaded submodule having a different copy
of `blendfile`.
Also loaded modules are logged more explicitly (at INFO level) to aid in
debugging later on.
The loading of modules from wheels wasn't properly separated from the rest
of Python yet. Now `load_wheel()` properly cleans up after itself, making
it impossible for other code to do `import the_module_from_the_wheel`.
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.
