re-enable link resolver, but fix the underlying issue in the "link changed" signal.

The feature itself still doesn't work for me, but this code does the same thing.
only thing that's really different is it also disconnects the signal properly once
the TextLayoutElement is deleted

src/messages/MessageElement.hpp

@@ -135,10 +135,11 @@ public:
     virtual void addToContainer(MessageLayoutContainer &container,
                                 MessageElementFlags flags) = 0;
 
+    pajlada::Signals::NoArgSignal linkChanged;
+
 protected:
     MessageElement(MessageElementFlags flags);
     bool trailingSpace = true;
-    pajlada::Signals::NoArgSignal linkChanged;
 
 private:
     QString text_;