GUI2/Grid: explicitly delete copy and move ctors

The base class (widget) copy ctor and assignment operator are deleted, but this is to try to fix
some test build errors with GCC.

src/gui/widgets/grid.hpp

@@ -33,6 +33,12 @@ class grid : public widget
 public:
 	explicit grid(const unsigned rows = 0, const unsigned cols = 0);
 
+	/** Delete the copy constructor. */
+	grid(const grid&) = delete;
+
+	/** Delete the move assignment operator. */
+	grid& operator=(const grid&) = delete;
+
 	virtual ~grid();
 
 	/***** ***** ***** ***** LAYOUT FLAGS ***** ***** ***** *****/