Add support for toggling Design Mode from JavaScript

With our legacy VSTO add-in it was possible to toggle the Design Mode button in the Developer tab on the ribbon. We are working with tagging content and would now like to accomplish the same through Office.js

Or at least somehow toggle all content controls to show as 'Bounding box' or as 'Start/End Tag'. We are reluctant to changing this state directly on each content control as this applies changes to the document.

Would be great to have this option also in the Office.js API