Set up for Heroku uniphil/commit--blog

Notably, psycopg2 and/or postgres are picky about types when filtering in queries.
In particular, Blogger.gh_id is stored as a string in the database, while GitHub's
responses provide it as in int, so it has to be casted to a string.

We could take GitHub's word for it and put ints in the database, but depending on
data types from external sources feels sketchy