Update dependencies

A lot of dependencies that were chosen in 2010/2011 are still in use and have not been updated.

For instance, those that include celery (ckanext-qa for example) are using a version from 2011 even though Celery has undergone many improvements. The `pika` in use by ckanext-harvest is also from the same time frame.

I don't think this is a huge task, beyond finding out which ones are out of date, and ensuring tests pass, it might be a good place for someone new to ckan to start?

Start with the dependency declarations for ckanext-qa and ckanext-harvest, focusing on the Celery and pika versions mentioned in the issue. Identify other outdated dependencies, check compatibility and run the relevant tests. Done means the selected dependencies are updated and the test suite passes.

Written by the indexing model from the issue text.