Vanishing stream sessions about blocktogether

[jsha]

Plan of attack here: Twitter streams emit an empty message "{}" every ~5 seconds while they are active. We ignore these keepalive messages currently, but as a debugging measure we should keep an in-memory last-updated timestamp for each stream, either stored as an extra field on the req stored in activeStreams, or in its own map. Timestamp gets updated with all messages even if they are ignored. In the periodic logger for how many active streams, map over the keys of activeStreams and log the user and age for any streams whose last-updated timestamp is >60 seconds.

[jsha]

Wound up punting on this and just adding a setTimeout on the stream, so if it doesn't get anything for 70 seconds, it aborts, which triggers a restart.