Basic Addons UI

This adds and auto loaded addons UI which processes all the addons defined in module-list.js and loads any that are marked as auto-load before displaying a list of loaded modules.  Any custom UIs not already loaded can be loaded by clicking on their name.

At the moment, the UI displays a window at startup, which is undesirable.  It can be closed (hidden) by clicking on the X icon however.  At this point I know of no way of re-showing the UI window.
Yes, intentionally so.  I wanted to PR that change separately.  I should have removed the link I guess but didn't bother as the browser will just ignore it.