Use tqdm for progress bars
This PR updates gwpy.utils.mp and adds a new module gwpy.utils.progress that uses tqdm for verbose progress bars.
This adds tqdm as a hard dependency for gwpy, which might be an issue for debian jessie.
UPDATE: this PR probably needs to sit here until python-tqdm is moved into production as part of the lscsoft jessie distributions. You can follow along here (required LIGO.ORG auth).