Automatically load/save Logger configs
based on state changes.
This particular implementation is intended to be efficient but imperfect.
Data, at least as far as high water marks, may be lost.
It monitors changes to Logger configs, and saves them to userscript
storage as appropriate.
If the userscript enables the value change listener API (see below), that
will be used to detect when values need to be reread. Otherwise, it will
use the browser based visibilitychange event to reload.
// Enable in the ==UserScript== header with:
// @grant GM.addValueChangeListener
// @grant GM.removeValueChangeListener