ENH: publish Particle device vitals on a cadence

[jschrempp]

Device vitals are an excellent way to track connectivity performance. Today we use the automated version which only publishes on a cloud connect event or when we manually refresh from the device console.

Devices can be set to publish vitals on a regular basis. Particle documentation says that these publications do NOT count against our monthly DO allocation.

Particle.publishVitals(3600); // Publish vitals each hour

Seems like an easy way to gather useful data.