wip: add md editor for scheme description.

app/lib/widgets/dde_markdown_field.dart

@@ -99,9 +99,11 @@ class _DMarkdownFieldState extends State<DMarkdownField> {
                   textFocusNode: _focusNode,
                   padding: EdgeInsets.symmetric(horizontal: 5),
                   onComplete: (content) {
+                    if (content == widget.initText)
                       setState(() {
                         _previewText = content;
                       });
+                    else
                       widget.onComplete(content);
                   },
                 ),