Hook up the PS2MouseDevice to the AbstractScreen+WindowManager.

Render the mouse cursor by xor'ing the pixels. I don't know anything about
hardware cursors yet and this way we don't need to recompose the window
hierarchy every time you move the mouse. :^)

Widgets/Point.h

@@ -28,6 +28,11 @@ public:
             && m_y == other.m_y;
     }
 
+    bool operator!=(const Point& other) const
+    {
+        return !(*this == other);
+    }
+
 private:
     int m_x { 0 };
     int m_y { 0 };