Don't take clips from the p06 platform

They don't exist for p06, so we were seeing flip-flopping between
ingests of PC and p06.
Merge pull request #414 from atlasapi/pmlsc-clips

Don't take clips from the p06 platform
Switch lookback for xbox pmlsc to -7 days, not -19
Batch PA writes into one per channel day

Many channels have lots of repeats of the same programme throughout
the day (think weather every 30 minutes). This can lead to some very
write-heavy periods with large items being updated repeatedly. Here
we are batching the writes such that an item and its hierarchy is
written at most once per channel day.
PA brand and series summaries must be written after content
Merge branch 'batch-pa-channel-day' into stage