add includes necessary to compile

src/dispatcher.h

@@ -1,6 +1,7 @@
 #pragma once
 #include <gtkmm.h>
 #include <mutex>
+#include <functional>
 #include <list>
 
 class Dispatcher {

src/menu.h

@@ -1,6 +1,7 @@
 #pragma once
 #include <string>
 #include <unordered_map>
+#include <functional>
 #include <gtkmm.h>
 
 class Menu {

src/selection_dialog.h

@@ -1,6 +1,7 @@
 #pragma once
 #include "gtkmm.h"
 #include <unordered_map>
+#include <functional>
 
 class SelectionDialogBase {
   class ListViewText : public Gtk::TreeView {

src/tooltips.h

@@ -2,6 +2,7 @@
 #include "gtkmm.h"
 #include <string>
 #include <list>
+#include <functional>
 
 class Tooltip {
 public: