Mailman Fixes

This PR fixes two issues with the current email script (from WIP 50):

1. The bin/mailman executable conflicts with bundler's binstub for the actual mailman gem, to address this we simply rename bin/mailman -> bin/mailman_worker.

2. Forego (Foreman in Go) errors out if mailman_worker accepts STDIN, this PR disables this. There is no user or dev facing impact to this change.