19622: Add checking for duplicates and overlaps in the schedules feed

Background

So far the feeds we got from dynamite had no duplicated broadcasts or overlaps, that's not the case with the iBL feeds since the nitro information has this issue. This is something being worked on Nitro. In the meantime, we need to make sure that our feeds are free of duplicates or overlaps.

https://jira.dev.bbc.co.uk/browse/IPLAYER-19622