Determine markings on non-plugin enriched content

[moorscode]

We currently determine the markings based on the content after plugins have added their content to the "content".

This will provide situations where marker-buttons are shown but the marked content is not visible in the editor, thus "nothing happens" when clicking the button.

If we determine the markings on the content that is provided by the default editing experience and maybe provide a callback for plugins to receive marked content when applicable, the user experience will be improved.

Possible steps:

• Don't show markings when they don't apply to the "editor content"
• Provide API to present marked content back to external parties (plugins)