Merge tag 'sparks-1.15.3' into develop

1.15.3
Don't use @with_remote_configuration in `git_pull()`, this fails on initial deployment, and is not strictly needed anyway.
supervisor/gunicorn: make the restart/reload supervisor commands more precise (don't reload  if there is no need to; don't even update if configuration files didn't change). Massive refactor to lower the supervisor function complexity.
More love on the git_pull+django_reload feature.
bump version in setup.py
Merge branch 'release/1.15.4'