Provide option to turn off CodeMirror for content textarea

CodeMirror's RTL handling makes editing content in the admin panel a pain once mixed languages or even Markdown is added to the text.

Removing the reliance on CodeMirror is probably too much to ask, but it would be nice to have the ability to paste text in the admin interface and do light editing without CodeMirror getting in the way.

Locate the admin panel's content textarea and the CodeMirror setup, then trace how that editor is initialized. Add an option that allows the textarea to be used without CodeMirror, and verify that pasting and light editing work in the admin interface while the existing editor behavior remains available.

Written by the indexing model from the issue text.