Twitter pack

First iteration includes a sensor which searches Twitter for recent tweets matching the criteria defined in the config. When a matching Tweet is found, a trigger is dispatcher.
This got me thinking - it seems like we could provide this functionality via the "sensor_service" which is passed to each sensor instance.

This functionality would allow sensor to persist state (on cleanup) and retrieve it (on set up) from a datastore. There is some overlap between this and what we have talked about "resumable" actions, but I view this is a way simpler thing. We don't enforce any structure or whatever, we just allow sensors to persist and retrieve stuff from the datastore via the sensor_service.

Anyway, this is something which needs more discussion in a different repo.