Allow message types to be disabled in PhutilConsole

Summary: I need this in order to implement a --json flag to arc unit without creating a big mess in the process.

Test Plan: Implemented a --json flag for arc unit, using disableOut() to disable normal output.

Reviewers: btrahan, vrana

Reviewed By: vrana

CC: aran

Maniphest Tasks: T2065

Differential Revision: https://secure.phabricator.com/D4213