actually I have an idea.
we can do this minifying when copying the application to the target assets/www/. This can avoid doing copying.

See code in customize.py
```
55   if app_root:
 56     assets_path = os.path.join(sanitized_name, 'assets')
 57     shutil.rmtree(assets_path)
 58     os.makedirs(assets_path)
 59     app_src_path = os.path.join(assets_path, 'www')
 60     shutil.copytree(app_root, app_src_path)
```