Refactor RDTreeWidgetDelegate into RichTextViewDelegate that is reusable

* This allows us to add rich text support much more easily into other itemviews
  like RDTableView.
* We set it up for debug messages so that resource links in debug messages can
  be linked.

qrenderdoc/Windows/DebugMessageView.ui

@@ -27,7 +27,10 @@
     <number>3</number>
    </property>
    <item>
-    <widget class="QTableView" name="messages">
+    <widget class="RDTableView" name="messages">
+     <property name="horizontalScrollBarPolicy">
+      <enum>Qt::ScrollBarAlwaysOn</enum>
+     </property>
      <property name="selectionMode">
       <enum>QAbstractItemView::SingleSelection</enum>
      </property>
@@ -53,6 +56,13 @@
    </item>
   </layout>
  </widget>
+ <customwidgets>
+  <customwidget>
+   <class>RDTableView</class>
+   <extends>QTableView</extends>
+   <header>Widgets/Extended/RDTableView.h</header>
+  </customwidget>
+ </customwidgets>
  <resources/>
  <connections/>
 </ui>