added Welcome page

changed settings API and page to React + rest
changed structure of scripts - different folders for editor and admin scripts

src/admin/pages/index.js

@@ -0,0 +1,21 @@
+/**
+ * WordPress dependencies
+ */
+import { __ } from '@wordpress/i18n';
+
+/**
+ * Internal dependencies
+ */
+import PageWelcome from '../page-welcome';
+import PageSettings from '../page-settings';
+
+export default {
+	welcome: {
+		label: __('Welcome', 'mind'),
+		block: PageWelcome,
+	},
+	settings: {
+		label: __('Settings', 'mind'),
+		block: PageSettings,
+	},
+};