Collapsable/hideable package metadata.

I'd like to suggest an alternative to the two-column layout that would benefit mobile/narrow window users too. If the metadata was collapseable/hideable and the last state was remembered in a cookie users that don't care about the metadata would only have to collapse it once and then not see it anymore, while those who care can just keep it open. A third condensed state would be nice where some important bits are shown like the currently viewed version.

Locate the package metadata and two-column layout entry points, then inspect how narrow-window presentation and cookie-backed state are handled. Done means metadata can be collapsed or hidden, optionally shown in a condensed state, and the chosen state is remembered for later visits.

Written by the indexing model from the issue text.