Ensure equivalated items in schedules only have one broadcast
Only write relevant broadcast to schedule store, dedupe content writes

Ensure that only the relevant broadcast, i.e. the one in the window,
is written to the schedule store.

When a piece of content appears multiple times in a schedule write it
will only be written once.
Merge pull request #12 from atlasapi/mbst-8009-broadcast-per-schedule-item

MBST-8009 broadcast per schedule item