Use celery task to validate GTFS feeds on upload.

Add celery, Rabbit MQ, and Google's feedvalidator.py to project.
Run feedvalidator on uploaded GTFS in asynchronous celery task.
Cleanup in response to feedback
Resolve merge conflicts in provisioning file
Merge pull request #5 from flibbertigibbet/feature/celery-upload

Use celery task to validate GTFS feeds on upload.
Get console output from feed validator and examine for errors/warnings.

Add field with validation summary to GTFSFeed model.
Check validity (valid if no errors) and write to is_valid field.
Saves results as text file of console output, instead of HTML.
Merge pull request #6 from flibbertigibbet/feature/parse-validation-results

Get console output from feed validator and examine for errors/warnings.