Move ::demandAttention to AbstractClient

abstract_client.h

@@ -110,6 +110,7 @@ public:
     virtual bool wantsInput() const = 0;
     virtual void checkWorkspacePosition(QRect oldGeometry = QRect(), int oldDesktop = -2) = 0;
     virtual xcb_timestamp_t userTime() const;
+    virtual void demandAttention(bool set = true) = 0;
 
     virtual void growHorizontal();
     virtual void shrinkHorizontal();

client.h

@@ -434,7 +434,7 @@ public:
     bool isDemandingAttention() const {
         return demands_attention;
     }
-    void demandAttention(bool set = true);
+    void demandAttention(bool set = true) override;
 
     void updateDecoration(bool check_workspace_pos, bool force = false);
     void triggerDecorationRepaint();