Introduce native Gutenberg controls

• Register meta
• Enqueue script
• Switch to use_block_editor_for_post_type and remove the option
• Build component
• Add sanitize callback to handle special cases
• Add auth callback to allow "private" meta to be edited
• Add padding between modal buttons
• Don't hide UI if set to 0, as there's no way to update the setting
• Switch to @wordpress/scripts
• Consider moving Gutenberg bits, and/or REST API elements, to their own class.

.distignore

@@ -4,6 +4,7 @@
 .git
 .gitignore
 .gitlab-ci.yml
+.nvmrc
 .travis.yml
 .wordpress-org/*
 .DS_Store
@@ -26,7 +27,7 @@ phpcs.xml
 .phpcs.xml.dist
 phpcs.xml.dist
 README.md
-assets/src/
+assets/src/*
 wp-cli.local.yml
 yarn.lock
 tests
@@ -35,3 +36,4 @@ node_modules
 *.sql
 *.tar.gz
 *.zip
+webpack.config.js