Restructure to run all sources, use assets and asset sensors

[valentinedwv]

This code:

1. read list of sources from a gleaner config in s3
2. runs the data loading for new sources

Needs to:

• add a scheduler based on a cron field in the gleaner config

ponder:

• upload the 'image' assets for a source (aka logo) to s3. That way we always have a copy.