Gutenberg integration

[jazzsequence]

Replace CMB2 entirely with Gutenberg.

All of the CMB2 fields could be rebuilt as G'berg blocks. This would allow editorial control over how recipes are displayed, rather than putting that burden on the theme -- which ultimately makes the plugin more universal on any theme and relies far less on filtering the_content to display recipe information. More importantly, though, an editor could rearrange recipe components however they wanted.

Some considerations

• [ ] Recipes have a specific formula. If blocks are used for everything, it might be easy to forget to add certain pieces of information that would be used on a recipe. Some sort of checklist or universal list of recipe information (possibly integrating with the Document inspector control) would be useful to remind the user to add things that are required
• [ ] The current API implementation uses custom routes, but G'berg uses register_meta and the default WP routes for meta that were added after this plugin was built. Would need to think about backwards compatibility and integration.
• [ ] Should we care about pre-G'berg WP and default to/include CMB2 until G'berg is merged?
• [ ] Is there anything that CMB2 does that is superior to anything that G'berg does?

[jazzsequence]

I'm not sure it makes sense to even use G'berg for everything -- maybe just the placement of particular sections or the recipe itself....although generally recipes appear below the post so maybe it's not even worth doing a g'berg integration to replace cmb2.

Maybe g'berg integration means creating a block to insert a recipe into another post or insert a list of recipes by a taxonomy.