idea: TinyMCE demo for A4 paper

It would be similar to the [word processor demo](https://tinymce.github.io/tinymce-demos/cool-demos/wordprocessor.html) but adjust the content area for a A4 paper sheet.

The A4 paper dimensions have a width of 842 points along with a height of 595 points. The page margins are not standardized but [iText](https://github.com/itext) uses 36 points.