closes#5433
- add gh-input class to inputs
- stop the incorrect addition of trash can on url page
- fix trigger of upload success to show loading in editor
- fix duplicate url field for images outside of editor when there is no file storage
closes#4368, fixes#1240 (spellcheck), fixes#4974 & fixes#4983 (caret positioning bugs)
- Drop CodeMirror in favour of a plain text area
- Use rangyinputs to handle selections cross-browser
- Create an API for interacting with the textarea
- Replace marker manager with a much simpler image manager
- Reimplement shortcuts, including some bug fixes