templates: tweak file edit page markup to be slightly more correct and make it look slightly better - use <label> for the commit message label - use .form-group - use form-inline only for the heading - use form-group-sm to make the <select> less bloated

# 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
.