Demote package URLs to a less prominent place

[djc]

Current Behavior

I noticed yesterday that these new package URLs have appeared in the sidebar:

These were implemented to appear on top, before the last release age, MSRV, license and size. The little info widget points to a GitHub repo which arguably does not clearly/obviously/easily convey why or how these URLs might be valuable to me as a Rust user.

Expected Behavior

These package URLs, while they might some day be useful, do not appear to have obvious utility for what I'd guess is probably a supermajority of crates.io users (Rust developers) today. As such, I think their appearance does not merit being at the current level of the information hierarchy -- at best, they should be at the bottom of that list, though it might be even better to move them to the bottom of the sidebar, beneath the Report button maybe?

[weihanglo]

Relevant discussion: #t-cargo > What to do with purl in Cargo docs, which is around how to make users understand it.