Fixes errors caused by special characters

[jeffdaley]

Applies a cleanString function to editable Document properties to replace invalid characters with ASCII-friendly equivalents. This fixes an error where creating or saving a doc with special characters, e.g., smart quotes, bullets, accented letters, would throw an error and sometimes delete the document header.

I consider this a short-term solution while we investigate how to make special characters work.

New dependency: https://www.npmjs.com/package/replace-special-characters