Style: Reduce space consumed by headers and improve alignment

[CAM-Gerlach]

As discussed on #2514 , the headers at the top consume excessive vertical space, particularly on mobile which some style tweaks could dramatically improve with no loss of information. Furthermore, there are some odd gaps and spacing between the various elements that could be fixed, and the title and PEP number is redundant and can be removed, as it is present no less than four other places (the main title, the breadcrumbs, the sidebar [as addressed by #2532], and the tab title).

To note, while it is included in the comparisons below, this PR defers the implementation of removing or abbr-ing the email address to a followup PR, as it may require a bit more discussion and is better done after #2484 is merged.

Desktop (Before/After)

Mobile (Before/Previous/Latest)

Fixes #2514

[hugovk]

Checked on desktop (Mac, Chrome) and mobile (Samsung S10, Chrome) and looks good.

I'm mindful we shouldn't be squashing things too tightly together, but this is fine.

Thanks!

[hugovk]

Thanks!