Support Polldaddy's short URL format as a whitelisted oEmbed provider.

Props donncha.
Fixes #28283.


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Viddler has had a new oEmbed endpoint for at least 10 months. Let us update to it.

Props garhdez.
Fixes #24296.

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Add CollegeHumor.com oEmbed support. Fixes #24497. Props johnzanussi.
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