get celery setup to work properly

- launch all related services with a single fig invocation
- simplify .env file generation
- need to define C_FORCE_ROOT environment variable because we're running
  celery workers as root
- split out flower app from app container into it's own container
- do not store celery results in database as that prevents workers from
  starting
added make target to create django superuser easily
updated nginx configuration

- updated nginx.conf based on default config file provided by nginx image
- override container's default nginx config file
- bind mount log folder for easy access