Allow specifying a value of `none for the :opt:selection_foreground`` which will cause kitty to not change text color in selections

Fixes #1358

kitty/main.py

@@ -122,6 +122,7 @@ def _run_app(opts, args):
     if not is_wayland and not is_macos:  # no window icons on wayland
         with open(logo_data_file, 'rb') as f:
             set_default_window_icon(f.read(), 256, 256)
+    load_shader_programs.use_selection_fg = opts.selection_foreground is not None
     with cached_values_for(run_app.cached_values_name) as cached_values:
         with startup_notification_handler(extra_callback=run_app.first_window_callback) as pre_show_callback:
             window_id = create_os_window(