Find a way to clean up arrays of subscriptions

[lawrence-forooghian]

In #19 the DefaultRoomStatus creates an array of Subscription objects to which it can emit status updates. We need a way to remove subscriptions from this array once they're no longer needed. In 20e7f5f I said that there might be a way to do this automatically based on some event (I’m being very vague here because I don't know what); let's look into that. Else we might need to introduce the unsubscribe methods from JS.

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