added sentry mode get/set as lockmechanism

[raffertyj]

followed convention followed by locks to use create sentry mode functionality. there's an async copy of the setter i didn't use here (setSentryModeAsync). there was also a status bool for sentry available but i figure all cars should have it, it can be disabled in config if it for some reason isn't working for someone

[raffertyj]

of note, i debated a toggle or lock mechanism, the lock seemed more apt.

[nfarina]

Looks awesome, thank you!