Single field editing

Here comes a bit of a status for this work:

We've now got a working editor for a text field as part of the standard node edit form.

There you can use all kinds of Gutenberg blocks within that editor and define settings and so on for each of them.

What remains:

• Style injections: Injecting styling from the frontend theme.
• Configuration of the text format: The UI for defining which blocks to be available, image styles and so on.

This is probably a couple workdays with testing, coming in the mid September release.