Made undo tool aware of circle count to decrement. Refactored tool ID's to be enum

src/widgets/capture/capturewidget.cpp

@@ -709,6 +709,10 @@ CaptureWidget::handleButtonSignal(CaptureTool::Request r)
       incrementCircleCount();
       break;
 
+    case CaptureTool::REQ_DECREMENT_CIRCLE_COUNT:
+      decrementCircleCount();
+      break;
+
     case CaptureTool::REQ_CLOSE_GUI:
       close();
       break;
@@ -796,6 +800,12 @@ CaptureWidget::incrementCircleCount()
   m_context.circleCount++;
 }
 
+void
+CaptureWidget::decrementCircleCount()
+{
+  m_context.circleCount--;
+}
+
 void
 CaptureWidget::setDrawThickness(const int& t)
 {