Allow DivinerPublisher to be specified as a flag
Summary: Allow the DivinerPublisher subclass to be specified via ./bin/divner generate --publisher .... In particular, this allows use of the (mostly broken) DivinerStaticPublisher.
Test Plan: Ran ./bin/diviner generate --publisher DivinerStaticPublisher
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D11588