This adds lots of commented out code that provides a settings panel
to add new library sources. It is incomplete as it doesn't actually
add/update the library sources on the runtime.
For 1.3, I'm focussing on allowing additional sources get added
via the settings file only. I've done enough work on the editor
side to convince myself more work is needed than I can justify
at this time on what is otherwise not going to be a widely
used feature.
