Fields UI initial scaffolding (#14)

* adds fields metakey

* adds basic webpack process with demo of fields modal

* basic state update for new fields

* initial pass at getting the fields to save data

* ui cleanup on the fields modal

* adds ability to delete field

* pulls post type name from constant

* move new field to separate modal

* move fields UI enqueue to separate function

* adds basic fields ui to single posts

* remove debugging code

* try listgroup instead of cards

* adds support for image field

* updates block inserter to match UI

* early return for CPTs with no fields

* clean up imports from webpack changes

Author: bacoords

build/manager/fields-ui.asset.php

@@ -0,0 +1 @@
+<?php return array('dependencies' => array('react', 'wp-components', 'wp-core-data', 'wp-editor', 'wp-element', 'wp-i18n', 'wp-plugins', 'wp-primitives'), 'version' => '503b3b31ed74435cd1d2');