Add option to show error tracebacks to user without logging everything

[vidartf]

Currently, if you start voila in --debug mode almost everything gets logged. It would be nice to have a way to enable traceback for "developer" dashboards deployments without having the logs be as verbose as they are. Currently they are linked one-to-one here:

voila/voila/execute.py

Lines 36 to 38 in 80b120c

	def should_strip_error(config):
	"""Return True if errors should be stripped from the Notebook, False otherwise, depending on the current config."""
	return 'Voila' not in config or 'log_level' not in config['Voila'] or config['Voila']['log_level'] != logging.DEBUG

A possibility would be to add a separate config option "send_tracebacks" that defaults to the current value (dependent on log level) if unset.

[SylvainCorlay]

Maybe show_tracebacks instead of send_tracebacks.

[vidartf]

Agreed. I would make a PR for this, but for the dev install on Windows a bunch of tests fail on master, so I assume Windows contributors are not supported 😉