Restore some Q_OBJECT macros (#516)

Reverts commit 08dfcc, and restores part of the changes.

This resolves #516 (closed).

GUI/View/Plot2D/ColorMapCanvas.h

@@ -27,8 +27,6 @@ class QCustomPlot;
 //! Controls appearance of the status string.
 
 class ColorMapCanvas : public QWidget {
-    Q_OBJECT
-
 public:
     explicit ColorMapCanvas(QWidget* parent = nullptr);