Move them into the module folder so that they'll be properly included
in distribution builds, such as when installing this module via pip.
Also reword copyright headers to refer to the project root instead of
the repository root, which isn't included in distribution builds.
Set license to multi-license of AGPL + Element Commercial, and add
associated license files to the repository root.
This does not add a notice of "This file includes modifications" to any
files because they were only moved and relicensed, but otherwise
unmodified.
The exception is run_in_venv.sh, which is a rewrite of upstream's
run_in_venv.js and thus lacks the original copyright entirely.
Andrew Ferrazzutti