WIP Organize, use RXJS for observableGrillStatus, use events, add tests.

[facultymatt]

Goal is to save events into database for things like

• grill on / off / fan mode / cold smoke mode
• grill / probe desired temp change
• low pellet alarm active
• desired temp reached

Approach is to make observable grill state, and use rxjs operators to know when conditions change, and save events into database.

Re-org based on https://softwareontheroad.com/ideal-nodejs-project-structure/, worked well for this project.

TODO

• Change to do lots of short connections to grill is proving less stable than in master, where we keep one grill connection open for getting status.
• strange unexpected events are getting into database like probTempChange with null temp. Need to debug this