Add ability to read onboard accelerometer and contribute to EEW network

[andygrillo]

To supplement areas without openeew sensors, it could be good to adopt the MyShake/Google method of crowdsourcing accelerations from user apps: https://blog.google/products/android/earthquake-detection-and-alerts/

Perhaps we could consider reading accelerations from this alerting app, and in the future sending them to the cloud when they become 'interesting'.