Improve plugin error output for debugging

Plugin errors will now include a snapshot of the JSON lock data provided to them by the main protolock executable. The JSON is written after a newline to separate it from the error reported. The intention is to provide users with the ability to capture and parse this output programmatically if needed.

Thanks to @milton0825 for sharing the use case and helping determine the error output format.

See #113 & #114 for more details.