Parameter for always expanded request / response panels

It would be nice to allow generating HTML files with expanded (and non-collapsible) requests and responses, so that you can just read the documentation without requiring expanding collapsed documentation items. It could be done by adding a template parameter and fixing the mixins file...

Start by locating the template and mixins file referenced in the issue, then trace how template parameters are passed when generating static HTML. Done means generated request and response panels can be configured as expanded and non-collapsible, while existing output remains unchanged by default.

Written by the indexing model from the issue text.