Quoted text remarkup should be smart enough to know when to add a '>' and when to add '> '

Summary: Fixes T8565, Quoted text remarkup should be smart enough to know when to add a '>' and when to add '> '

Test Plan: Open an object with remarkup comments, add 'quote', select that text click the quote button in the remarkup menu, text should become '> quote'. Select and click again, text should become '>> quote'.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T8565

Differential Revision: https://secure.phabricator.com/D13334