Re #6807. Add log warning on unfulfilled request for historical data.

If an event-based live listener does not support historical data, then
tell the user that they're only going to be getting data from the
algorithm launch time onwards.
Re #6807. Use non-stream logger for fixed string.

Also set the start time to zero rather than the current time, for
consistency with what's done above. The end result will be the same.
Re #6807. Make comments more general.

The previous comments don't belong in this general class as they were
talking about very specific SNS/ADARA/SMS things.
Re #6807. Correct the supportsHistory value on the SNS listener.
Merge remote-tracking branch 'origin/feature/6807_livedata_supportshistory_check'