initialize blank editor set in EditorManager; update overworld initialization to use Rom pointers; add Clear and CleanupUnusedTextures methods in OverworldEditor.

src/app/editor/editor_manager.cc

@@ -73,6 +73,11 @@ void DrawRomSelector(EditorManager &editor_manager) {
 }  // namespace
 
 void EditorManager::Initialize(const std::string &filename) {
+  // Create a blank editor set
+  auto blank_editor_set = std::make_unique<EditorSet>();
+  editor_sets_[nullptr] = std::move(blank_editor_set);
+  current_editor_set_ = editor_sets_[nullptr].get();
+
   if (!filename.empty()) {
     PRINT_IF_ERROR(OpenRomOrProject(filename));
   }

src/app/editor/graphics/graphics_editor.h

@@ -169,7 +169,7 @@ class GraphicsEditor : public Editor {
 
   Rom temp_rom_;
   Rom tilemap_rom_;
-  zelda3::Overworld overworld_{temp_rom_};
+  zelda3::Overworld overworld_{&temp_rom_};
   MemoryEditor cgx_memory_editor_;
   MemoryEditor col_memory_editor_;
   PaletteEditor palette_editor_;

src/app/editor/overworld/overworld_editor.h

@@ -86,7 +86,10 @@ class OverworldEditor : public Editor, public gfx::GfxContext {
   absl::Status Paste() override { return absl::UnimplementedError("Paste"); }
   absl::Status Find() override { return absl::UnimplementedError("Find"); }
   absl::Status Save() override;
+  absl::Status Clear() override;
 
+  void CleanupUnusedTextures(uint64_t current_time, uint64_t timeout) override;
+  
   int jump_to_tab() { return jump_to_tab_; }
   int jump_to_tab_ = -1;