Remarkup - add a quote button

Summary: Fixes T7696.

Test Plan: hit the quote button with no text - it worked. highlighted some text and hit the quote button - it worked. hit the list item button with no text - it worked. hit the list item button with text selected - it worked

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7696

Differential Revision: https://secure.phabricator.com/D13060