implement android import, update android project and build for release

src/app_events.cpp

@@ -3,6 +3,7 @@
 
 #ifdef __ANDROID__
 void displayKeyboard(android_app* mApplication, bool pShow);
+void pick_file(android_app* mApplication, std::function<void(std::string)> callback);
 #elif _WIN32
 std::string win32_open_file();
 #endif
@@ -55,7 +56,7 @@ void App::pick_image(std::function<void(std::string path)> callback)
             callback(path);
     });
 #elif __ANDROID__
-    //displayKeyboard(and_app, false);
+    pick_file(and_app, callback);
 #elif _WIN32
     std::string path = win32_open_file();
     if (!path.empty())