Added config file functionallity to allow user specific settings when called by apt-hook

desktop-menu needs to read individual settings from a config file to avoid user specific menu configurations getting overwritten when script is called automatically by apt hook.

This version keeps full backward compatibility to --wirite-out-global from apt-hook.

The new functionallity will be only noticable once a settings file was created and the --autoread-config setting was stored in it. Otherwise it will behave exactly as all version before.

See updated help file text for usage details.