front-end: Store temporary files in a tmp directory Avoid mixing temporary files with source files or have them in the generated output. But for now, keep them in the front-end directory where we need write access for node_modules anyway.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.