mattdrayer/multitenant-fulfillment: Add partner code support

* mattdrayer: Enable site-level overrides for all settings
* mattdrayer: Update edx-lint to 0.5.1
* mattdrayer: Increment minor version

Update the pypi password (ECOM-3912)

Corrected base.txt requirements

Updated the file to account for the fact that this is both a library and an application.

ECOM-3860

Replaced ecommerce-api-client with edx-rest-api-client

ECOM-3860

ECOM-3860

ECOM-3860

Bump version to 0.3.1

Use heartbeats and disable connection pooling to prevent broker connection loss

When the broker is behind a load balancer, the load balancer may timeout Celery's connection to the broker, causing messages to be lost.

Fix service_variant label used for logging

We use an rsyslog DynaFile template to look for the service_variant label in log messages and dump them to /edx/var/log/<service_variant>/edx.log. Since the service_variant used here was the old 'ecommerce_worker', logs were being dumped to the wrong location on disk. This is half of a larger problem with ecomworker logging, the other half being forwarding the correct logs Splunk. ECOM-3496.

Specify queue to consume at worker startup

Avoid initialization of Celery when used as a package

Previously, a cascade of imports caused a Celery app to be initialized whenever a shared task was imported. This is undesired: the application calling the shared task should be allowed to initialize and use its own Celery app. ECOM-2249.

Switch to Codecov

Enable authentication via JWT for ecommerce workers.

ECOM-2331

Configure Travis to deploy to PyPI when tags are pushed

Log warnings instead of errors when a task fails but can be retried

Prevent Celery from removing handlers on the root logger.

Allows setting custom logging handlers. Also fix service variant name.

fix

Add New Relic agent as an optional dependency

Asynchronous order fulfillment

Implements the ecommerce worker and a Celery task responsible for managing order fulfillment. ECOM-2242.