Gutenberg support

[frozzare]

I open this issue to start logging issues that Papi has with Gutenberg. I have fixed some issues in feature/gutenberg to make it work when saving.

I will happy to accept contributions to make Papi work with Gutenberg.

I personally haven't started using Gutenberg and therefor don't see all issues that this plugin have with Gutenberg. I have no intentional to make this plugin work with Gutenberg blocks (right now, maybe later) and I think it should start out as a separated plugin and then be merged to core.

This plugin should work without Gutenberg for those that don't want Gutenberg for various reasons

[frozzare]

https://core.trac.wordpress.org/ticket/45283

[frozzare]

• edit_form_after_title action is back since 5.0.2 so we don't need any fix for that.
• Autosaving don't work as expected.
• Editor property works with Gutenberg again.

[frozzare]

Hook into WP's new autosaving JavaScript if Gutenberg is active: https://github.com/WordPress/wordpress-develop/blob/master/src/js/_enqueues/wp/autosave.js#L375