KASM-1871 Add smooth scrolling

Previously all scrolling relied on "clicking" the up/down or left/right scroll buttons
which made it unprecise and to always scroll at the same speed.

Now we pass the scroll delta directly to the xorg input driver so the scroll is more responsinve and adaptive.

common/rfb/InputHandler.h

@@ -38,7 +38,9 @@ namespace rfb {
     virtual void pointerEvent(const Point& __unused_attr pos,
 		              int __unused_attr buttonMask,
                               const bool __unused_attr skipClick,
-                              const bool __unused_attr skipRelease) { }
+                              const bool __unused_attr skipRelease,
+                              int scrollX,
+                              int scrollY) { }
     virtual void clientCutText(const char* __unused_attr str,
                                int __unused_attr len) { }
   };