Extract out most code for text-with-ResourceId-links from RDTreeWidget

* The RDTreeWidget items still use this code, but it can now be reused
  on other widgets like RDLabel.

qrenderdoc/Code/qrenderdoc.cpp

@@ -179,6 +179,8 @@ int main(int argc, char *argv[])
 
   QApplication application(argc, argv);
 
+  RegisterMetatypeConversions();
+
   {
     PersistantConfig config;