delete objects on canvas with del

src/ui/view/GUI.java

@@ -310,6 +310,30 @@ public class GUI<E> implements CategoryListener {
 			}
 		});
 
+		String delDown = "delete";
+		inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_DELETE, 0, false), delDown);
+		actionMap.put(delDown, new AbstractAction() {
+			@Override
+			public void actionPerformed(ActionEvent e) {
+				for (CpsObject cps : model.getSelectedCpsObjects()) {
+					controller.delCanvasObject(cps);
+				}
+				model.getSelectedCpsObjects().clear();
+				//controller.setSelectedObjectID(0);
+					for (int i = tableModelHolonElementMulti.getRowCount() - 1; i > -1; i--) {
+						tableModelHolonElementMulti.removeRow(i);
+					}
+					for (int i = tableModelHolonElementSingle.getRowCount() - 1; i > -1; i--) {
+						tableModelHolonElementSingle.removeRow(i);
+					}
+					for (int i = tableModelProperties.getRowCount() - 1; i > -1; i--) {
+						tableModelProperties.removeRow(i);
+					}
+				canvas.repaint();
+				unitGraph.empty();
+			}
+		});
+		
 		frmCyberPhysical.setJMenuBar(menuBar);
 
 		frmCyberPhysical.setIconImage(new ImageIcon(this.getClass().getResource("/Images/Dummy_House.png")).getImage()