Toggle table header row/column icons

[abeforgit]

Is your feature request related to a problem? Please describe the use case and problem it solves.
For the editor, we've added a feature to toggle the first row or column of a table to be a "header" row/column.

Describe the solution you'd like
We'd like icons to go along with the toolbar menu items

Which project(s) or feature(s) is this related to
ember-rdfa-editor, frontend-gelinkt-notuleren, frontend-reglementaire-bijlage, other projects that use the editor