MC-4137: TinyMCE Issues within inline WYSIWYG

- Update lightgrey theme and add “magento” theme as legacy theme

Author: davemacaulay

lib/web/mage/adminhtml/wysiwyg/tiny_mce/tinymce4Adapter.js

@@ -193,6 +193,7 @@ define([
             settings = {
                 selector: '#' + this.getId(),
                 theme: 'modern',
+                skin: 'magento',
                 'entity_encoding': 'raw',
                 'convert_urls': false,
                 'content_css': this.config.tinymce4['content_css'],
@@ -263,6 +264,10 @@ define([
                 }
             };
 
+            if (this.config.skin) {
+                settings.skin = this.config.skin;
+            }
+
             if (this.config.baseStaticUrl && this.config.baseStaticDefaultUrl) {
                 settings['document_base_url'] = this.config.baseStaticUrl;
             }