Allow PhutilConsoleProgressBar to be quiet

Summary:
This allows you to use the progress bar even if you don't want it to output anything. This can simplify logic in other parts of your code.

$progress = new PhutilConsoleProgressBar();
$progress->setQuiet(true);
// etc.

Test Plan: derpy

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9586