Prevent keyboard trap in lesson editor

[jrobind]

Currently if you tab into the editor you cannot tab out of it. This causes a keyboard trap which is bad accessibility.

Essentially, we need to prevent WCAG 2.1.2 No Keyboard Trap.

A possible solution is to allow the escape key to exit the editor.

After some discussion in the Discord channel we might want to approach this by:

• adding a checkbox that allows you to enable/disable tab inside the quill editor. Once active you'll need to press esc (or click) to deactivate tab allowed mode
• alongside a checkbox, we might also need an onscreen message informing the user that hitting escape will allow them to tab to the next element.