Re-add pika, celery and tornado dependencies

These were correct in the 9d48b8a2cb012cb4f127a6918a2e251b4e497546
commit, but got dropped in the
ccfcb7f7cfa2f91d5cdfc1d3dfe0dd3931fb690c merge
Merge pull request #35 from rbu/readd-dependencies

Re-add pika, celery and tornado dependencies