[Bug 1089770] Simplify question/answer serialization + filtering.

Having no content in the list views has turned out to be a bit annoying, and removing it to save bandwidth proved to be a premature optimization. This simplifies the serializer situation for Questions and Answers by only having one that includes everything. Additionally, it fixes filtering by creator and question on Answers, since this is related to the reason we are putting answer content in the list view.

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