Consumers refactoring

This is ready for a review

Main changes:
- Pulled out the buildbot-related logic from PulseConsumer
- Changed the layout of pulse_consumer app to a more generic [etl](http://en.wikipedia.org/wiki/Extract,_transform,_load)
- Add an adapter for buildapi pending jobs
- Add a task to process pending jobs. We can potentially use a celery periodic task to run this task every minute or so

@camd @jeads any comment/suggestion would be very appreciated