remove $core_config['menu'] and let $menu_config be global config for menus
replace $core_config['icon'] with $icon_config
replace $core_config['plugin'] with $plugin_config
missed changes on replacing $core_config['plugin'] with $plugin_config
replace $core_config['user'] with $user_config
MAJOR: introduce several global variables other than $core_config, they are: $icon_config, $menu_config, $user_config and $plugin_config