Capture diagnostics to zip file

The `captureDiagnostics` command would capture many log files and place
them in a temporary folder, then present that folder to the user. The
most common use case for capturing diagnostics is to share them, so zip
the diagnostics up in to a more easily sharable .zip file.

Adds some tests to flesh out coverage on `captureDiagnostics`.

Author: plemarquand