Host runner improvements for automated testing

[ia0]

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The host runner currently provides the following simple user interface:

• Applet debug is written to standard output.
• Buttons are controlled by writing commands to standard input.
• LEDs status is updated by printing to standard output.

There is also a Web UI that provides a visual interface for those 3 components.

This issue would add some automatable UI by providing control over those components through sockets. A driver program could then interact with the host runner through those sockets to drive testing and fuzzing.