Normaliser pipe: Schedule

[rhiaro]

Need to finish pipe to transform Schedule data into a NormalisedEvent. Work has started, including pseudocode for the steps, here: https://github.com/openactive/harvester/blob/normalise-schedule/src/lib/pipes/normalise-schedule-pipe.js

[thill-odi]

This has become more urgent because the pipelines at the moment don't do anything with the structure SessionSeries -> SubEvent.