Add an optional editor toolbar

[vkbo]

Summary:

This PR adds a small vertical toolbar to the document editor that is hidden by default, but can be expanded by clicking the three dots icon in the editor header. The three dots icon replaces the edit label button that was there before.

The toolbar gives easy access to simple text formatting, with an option to toggle between Markdown or Shortcodes fo the overlapping formats.

Related Issue(s):

Closes #1585

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed