add changelog dialog and display_file api (implemented in osx and ios)

src/app_dialogs.cpp

@@ -4,6 +4,7 @@
 #include "node_dialog_browse.h"
 #include "node_dialog_cloud.h"
 #include "node_about.h"
+#include "node_changelog.h"
 
 std::shared_ptr<NodeProgressBar> App::show_progress(const std::string& title)
 {
@@ -18,6 +19,18 @@ std::shared_ptr<NodeProgressBar> App::show_progress(const std::string& title)
     return pb;
 }
 
+void App::dialog_changelog()
+{
+    auto dialog = std::make_shared<NodeChangelog>();
+    dialog->m_manager = &layout;
+    dialog->init();
+    dialog->create();
+    dialog->loaded();
+
+    layout[main_id]->add_child(dialog);
+    layout[main_id]->update();
+}
+
 void App::dialog_about()
 {
     auto dialog = std::make_shared<NodeAbout>();
@@ -29,6 +42,7 @@ void App::dialog_about()
     layout[main_id]->add_child(dialog);
     layout[main_id]->update();
 }
+
 void App::dialog_newdoc()
 {
     auto show_dialog = [this] {