Adjust PredictiveMaintenanceSettings

[OBerghmans]

Make phone and preferred_channel optional in predictive maintenance setting:

• Phone is not always filled in. Fixes my issue (MissingField in PredictiveMaintenanceSettings homeassistant-myskoda#34)
• Preferred Channel is also not always present. Fixes issue (unexpected error prédictive maintenance  homeassistant-myskoda#33)

Also made the "phone" print nicer when using the CLI (prints a "-" instead of None)

[WebSpider]

lgtm, waiting for linter to clear up

[OBerghmans]

Linting fails on the scripts directory. I can add the new line at the end of the python script, but I don't know how you would like to solve the namespace-packages finding.

[dvx76]

Linting fails on the scripts directory. I can add the new line at the end of the python script, but I don't know how you would like to solve the namespace-packages finding.

Not something you touched in this PR so no concern. It's just been fixed in another PR anyway I think. Thanks for contributing!