improve UI feedback when cancelling a task

app/widget/taskview/elapsedcounterwidget.cpp

@@ -65,6 +65,11 @@ void ElapsedCounterWidget::Start(qint64 start_time)
   UpdateTimers();
 }
 
+void ElapsedCounterWidget::Stop()
+{
+  elapsed_timer_.stop();
+}
+
 void ElapsedCounterWidget::UpdateTimers()
 {
   int64_t elapsed_ms, remaining_ms;

app/widget/taskview/elapsedcounterwidget.h

@@ -40,6 +40,9 @@ public:
   void Start();
   void Start(qint64 start_time);
 
+public slots:
+  void Stop();
+
 private:
   QLabel* elapsed_lbl_;