Add backend_url and broker_url to celery section of config

[dmlb2000]

Description

This adds a new default section to the config file celery and puts the backend_url and broker_url as environment variables previously referenced in the tasks module.

Signed-off-by: David Brown dmlb2000@gmail.com

Issues Resolved

Fix #50

Check List

• [ ] All tests pass. See https://github.com/pacifica/pacifica-docs/blob/master/development/TESTING.md
• [ ] New functionality includes testing.
• [ ] New functionality has been documented in the README if applicable