Add undo / redo command

The undo/redo command of diagram editor is
shared to the terminal strip editor.

sources/TerminalStrip/terminalstrip.cpp

@@ -1037,8 +1037,10 @@ bool TerminalStrip::fromXml(QDomElement &xml_element)
 				}
 			}
 
-			auto raw_ptr = new PhysicalTerminal(this, real_t_vector);
-			m_physical_terminals.append(raw_ptr->sharedRef());
+            if (!real_t_vector.isEmpty()) {
+                auto raw_ptr = new PhysicalTerminal(this, real_t_vector);
+                m_physical_terminals.append(raw_ptr->sharedRef());
+            }
 		}
 
 	}

sources/TerminalStrip/ui/terminalstripeditorwindow.cpp

@@ -55,6 +55,11 @@ TerminalStripEditorWindow::TerminalStripEditorWindow(QETProject *project, QWidge
     m_project(project)
 {
 	ui->setupUi(this);
+    if (auto diagram_editor = QETApp::diagramEditor(project)) {
+        ui->m_tool_bar->addSeparator();
+        ui->m_tool_bar->addAction(diagram_editor->undo);
+        ui->m_tool_bar->addAction(diagram_editor->redo);
+    }
 	ui->m_remove_terminal->setDisabled(true);
 	addTreeDockWidget();
 

sources/TerminalStrip/ui/terminalstripeditorwindow.ui

@@ -33,12 +33,12 @@
      <x>0</x>
      <y>0</y>
      <width>1364</width>
-     <height>21</height>
+     <height>23</height>
     </rect>
    </property>
   </widget>
   <widget class="QStatusBar" name="statusbar"/>
-  <widget class="QToolBar" name="toolBar">
+  <widget class="QToolBar" name="m_tool_bar">
    <property name="windowTitle">
     <string>toolBar</string>
    </property>

sources/qetdiagrameditor.h

@@ -54,6 +54,8 @@ class KAutoSaveFile;
 class QETDiagramEditor : public QETMainWindow
 {
 	Q_OBJECT
+
+        friend class TerminalStripEditorWindow;
 	
 	public:
 		QETDiagramEditor(