Add an option to use RichText instead of StyledText.

This fixes empty space issue at a cost of reduced performance.

qml/form/SettingGeneralForm.qml

@@ -4,6 +4,7 @@ import QtQuick.Controls 2.2
 Page {
     property alias lazyLoad: lazyLoadSwitch.checked
     property alias asyncMessageDelegate: asyncMessageDelegateSwitch.checked
+    property alias richText: richTextSwitch.checked
 
     Column {
         Switch {
@@ -14,6 +15,10 @@ Page {
             id: asyncMessageDelegateSwitch
             text: "Force loading message delegates asynchronously"
         }
+        Switch {
+            id: richTextSwitch
+            text: "Use RichText instead of StyledText"
+        }
 
         Button {
             text: "Invoke GC"