Issue 143 allow playable game width and height to be null

[laurenpudz]

Change Summary

[Briefly summarise the changes that you made. Just high-level stuff]

Change Form

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• The pull request title has an issue number
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Other Information

[Is there anything in particular in the review that I should be aware of?]

• allowed null/blank for game embed height and width
• added validation on the model that if the playable game ID is not null then both the game width and height must be non null
• refactored gameEmbedID to gamePlayableID on the frontend to match the field name used on the backend (was producing an undefined gameEmbedID value before that was breaking stuff)
• changed logic to check when game embed should now render. Will now only render when gamePlayableID, gameWidth and gameHeight are truthy (so filter out if any are null/undefined, 0, False etc...)

^ validation on admin site (if height is filled out but width is left blank, the width box will show an error the same way)

Related issue

• Resolve allow playable game width and height to be null #143