richtextdialog: show html tags rather than wysiwyg

While good in theory, a WYSIWYG rich text editor for large video frames
was unwieldy (and in many cases unhelpful). Instead the titler will
show plain text/HTML tags so the user can still write rich text but
without the unwieldy UI.

For a true WYSIWYG experience, we would probably need to write a true
graphical editor (a la Premiere's titler), but that's a later goal.
This titler will be sufficient in a good majority of cases and there
are plenty of dedicated graphics packages if more complex titling is
required for the timebeing.

app/widget/nodeparamview/nodeparamviewrichtext.cpp

@@ -48,8 +48,10 @@ void NodeParamViewRichText::ShowRichTextDialog()
 {
   RichTextDialog d(line_edit_->text(), this);
   if (d.exec() == QDialog::Accepted) {
-    line_edit_->setText(d.text());
-    emit textEdited(d.text());
+    QString s = d.text();
+
+    line_edit_->setText(s);
+    emit textEdited(s);
   }
 }