Add Load method to editor classes and update corresponding headers

src/app/editor/message/message_editor.cc

@@ -85,6 +85,10 @@ void MessageEditor::Initialize() {
   DrawMessagePreview();
 }
 
+absl::Status MessageEditor::Load() {
+  return absl::OkStatus();
+}
+
 absl::Status MessageEditor::Update() {
   if (rom()->is_loaded() && !data_loaded_) {
     Initialize();

src/app/editor/message/message_editor.h

@@ -38,6 +38,7 @@ class MessageEditor : public Editor, public SharedRom {
   MessageEditor() { type_ = EditorType::kMessage; }
 
   void Initialize() override;
+  absl::Status Load() override;
   absl::Status Update() override;
   void DrawMessageList();
   void DrawCurrentMessage();