Allow caching of generated ebook formats

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When click on generating an ebook from the page, drop q parameter to allow it to be cached. Additionally, adjust the service provider caching rules to ensure the page is cached and therefore won't be generated again

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It's done for Gutenberg Australia project: cd96d32

It's not applicable for the project Gutenberg.

For web may not make much of sense. But for news, it can be enforced. However, it's better first to refactor news section to avoid facing too much 403 or 401.