templates: cleanup index page and make repo group table a 'DataTable' as well The repo group table could be data based like the repo table instead of wrapping an existing table - that is not done here and could be done later. The unused reference to _dt_elements.html is removed.

# 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
.