perf(youtube-player): triggering change detection for unused events

[crisbeto]

Currently the YouTube player component events all trigger change detection and are registered ahead of time, even if they aren't being used. These changes only set up the events if somebody is subscribed to them.

Also fixes a case where first was being used instead of take(1). We want to avoid first, because it'll throw if the observable completes before emitting.

[jelbourn]

LGTM

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