Extracting external sites

[bmenn]

We need functionality to identify other potential sites to scrape.

[bmenn]

If someone get to this before I get back to this, we could use SQLAlchemy data model objects to simplify data access (but this does not mean less code).

http://docs.sqlalchemy.org/en/latest/orm/extensions/automap.html?highlight=automap#module-sqlalchemy.ext.automap

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[bmenn]

@dlrobertson @egrossman

Not 100% done here, but almost. Need to add a simple integration test and I'll be good. There's also an example of unit testing a Luigi task as well.

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