Fixes sudo, UI, duplicate point plotting issues

[byteit101]

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UI & Sudo & Duplicate Point fixes

I think the UI repainting is fully fixed here. I'm not confident of sudo/paplay yet.

UI + Scan background thread

The scan method now launches a background thread, if not already launched, to do the work of scanning. This makes the UI interactive and keeps desktop environments happy. I had to setup a pubsub thread callback mechanism as the scan background thread wants to repaint and update the status.

Sudo + paplay ding

This works, in some environments. I need to fix the other environments and/or document. Feedback appreciated. The UI drops permissions ASAP once it launches the scan subprocess. Communication is via JSON and a Scanner proxy object. Also a security win.

Plotting duplicate points

Duplicate points cause fun patterns, but useless output. Now they are filtered out