add --config flag to modify config path

+ use getters instead of constants in settings classes
+ refactor previous references
+ move get_xdg_config_dir() from settings.py to app.utils.xdg_utils.py

app/start_info_logger.py

@@ -44,7 +44,7 @@ def log_startup_info():
         )
 
     print(
-        f"{TCOLOR.YELLOW}Data folder: {Paths.APP_DIR}{TCOLOR.ENDC}"
+        f"{TCOLOR.YELLOW}Data folder: {Paths.get_app_dir()}{TCOLOR.ENDC}"
     )
 
     print("\n")