Formatted Canned Responses

Centralize how canned responses are formatted
Add ability to quote original and last messages as a canned response
Add JSON encoder utility to Format class
Add ticket thread quotes to canned responses

Add original and last message quotes to canned responses
Style blockquote for ticket thread
Enable canned responses by default
Review fixes
Merge pull request #1010 from protich/feature/canned-resp

Canned responses revisited

Reviewed-By: Jared Hancock <jared@osticket.com>