fix some ui glitch with NodeButton, start implementing working dir option

src/app.h

@@ -37,7 +37,7 @@ class App
 public:
     static App I;
     std::string data_path{ "." };
-    
+    std::string work_path{ "." };
     std::string rec_path{ "." };
     std::thread rec_thread;
     bool rec_running = false;
@@ -95,6 +95,7 @@ public:
 #endif
     void pick_image(std::function<void(std::string path)> callback);
     void pick_file(std::vector<std::string> types, std::function<void(std::string path)> callback);
+    void pick_dir(std::function<void(std::string path)> callback);
     void display_file(std::string path);
     void showKeyboard();
     void hideKeyboard();