This PR will...

• Force schedule update on asset or interstitial error
• Flush and clear assets when seeking back to earlier asset in interstitial

Why is this Pull Request needed?

Forcing an update handles cases where playout duration is not changed by error but schedule update is needed.
Flushing and clearing asset players when seeking back to an earlier asset handles shifts in the timeline cause by faulty assets earlier in the event.

Are there any points in the code the reviewer needs to double check?

Resolves issues:

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md