Re #7822. Add a method to clear all but the last value.

This will modify a TimeSeriesProperty to keep only the last entry. Note
that 'last' means the last added, unless the property has been sorted
first.
Re #7822. A method to clear all log values except the current one.

Takes all TimeSeriesProperty logs and clears out all entries
except the last one. Single value logs are left unchanged.
Re #7822. Keep the last log entries instead of clearing.

The previous way presented problems with unchanging or
slowly varying logs as a chunk could be left with an empty
log that the analysis relied on having.
The particular problem one was 'EnergyRequest', which was
only appearing in the first chunk.
I think that we can count on the logs coming in in time order, so the
fact that the underlying methods don't check or sort should not be a
problem.
Re #7822. Remove hoop jumping.

We no longer need this now the live listener has been updated to carry
over the current value of all logs.
Merge remote-tracking branch 'origin/feature/7822_carry_log_state_to_new_live_chunk'