Add support to display validation results

This merge request adds support to view the validation results for uploaded GTFS data by using Google's GTFS validator directly.

A number of changes were necessary to make this possible
 - updating provisioning script to include starting celery workers as daemon processes
 - creating a new `tasks.py` in the datasources app
 - setting up the front-end angular app to handle viewing upload results with basic stylings
 - adding a new `GTFSFeedProblem` model to store validation results
 - refactoring bower/grunt setup to include compiling scss into css for development