Add history to Clear Guides

src/canvas_modes.cpp

@@ -538,6 +538,13 @@ void CanvasModeGrid::commit()
 
 void CanvasModeGrid::clear()
 {
+    auto a = new ActionModeGrid;
+    a->m_mode = this;
+    a->m_highlight = m_highlight;
+    a->m_selected_index = m_selected_index;
+    a->m_lines = m_lines;
+    ActionManager::add(a);
+
     m_lines.clear();
 }