timebasedwidget: rewrote scroll catchup code

Code is much better. Less hacky queuing, implements cooldowns to improve navigation, and introduces a framework so that subclasses can make use of catchup/cooldown code too with any scrollbar they want

app/widget/keyframeview/keyframeview.cpp

@@ -290,8 +290,7 @@ void KeyframeView::mouseMoveEvent(QMouseEvent *event)
 
   if (event->buttons()) {
     // Signal cursor pos in case we should scroll to catch up to it
-    QPointF scene_pos = mapToScene(event->pos());
-    emit Dragged(scene_pos.x(), scene_pos.y());
+    emit Dragged(event->pos().x(), event->pos().y());
   }
 }
 
@@ -309,6 +308,7 @@ void KeyframeView::mouseReleaseEvent(QMouseEvent *event)
     selection_manager_.DragStop(command);
     KeyframeDragRelease(event, command);
     Core::instance()->undo_stack()->push(command);
+    emit Released();
   } else if (selection_manager_.IsRubberBanding()) {
     selection_manager_.RubberBandStop();
     Redraw();