TinyMCE editor for HTML textareas (except description)

Textareas with HTML enabled - except the description field - should be
editable with a (simple) rich text editor. This allows also users
without HTML skills to create formatted text. The description field is
excluded to ensure a working layout with this common field.

These are just some quick changes working well for our use cases.
Probably there's a more elegant implementation possible.

assets/css/um-styles.css

@@ -428,6 +428,16 @@ p.um-notice.warning {
 	outline: none !important;
 }
 
+.um-form .wp-editor-container {
+	border: 1px solid #ddd;
+}
+
+.um-form .wp-editor-container textarea {
+	background: #ddd !important;
+	color: #222 !important;
+	border-radius: 0;
+}
+
 /*
 	- Radio & Checkboxes
 */