Improve quote insert handler

[PHPirates]

Fixes #1425

Summary of additions and changes

• Don't replace quotes after a backslash, so you can always type \"
• Handle insertion at end of document properly
• Assume opening quotes are needed for csquotes whenever a close brace is not next

How to test this pull request

test typing \enquote{quoted} text and ``ligatures'' and \lq\lq{}commands\rq\rq{} and "offf"

Wiki

• Updated the wiki