UI state is somewhat confusing when viewing earlier requests

In #2216 I observed that the toolbar state can appear inconsistent after using the History panel and switching to an earlier request.

When switching, everything in the toolbar updates to show the data for the earlier request except for the subtitle in the History toolbar item itself.

In this example, after /eligibility/ loaded, I opened the History panel and switched back to the / request:

Everything else in the toolbar updates (the visible ones are things like like the Time, Request, SQL, and Templates), but the History item continues to show /eligibility/, which I found somewhat confusing.

Then, when you close whatever full page panel you're looking at, the state of the app is still at the current request, but the data being shown in the toolbar (aside from the History item) remains showing the older request that had been switched to.

Finally, one other minor issue is that if you switch away from the History panel and then reopen it, the older request you switched to is no longer highlighted.

In discussion with @tim-schilling and @VeldaKiara at DCUS sprints yesterday, we agreed that the following should be done at minimum:

• Change the History item's subtitle when switching to an older request
• After switching to an older request, keep it highlighted if you leave the History panel and come back

What needs further exploration: possibly introducing some additional notification to make it more obvious when the toolbar is showing data for an older request, and possibly introduce some kind of "take me back to the latest request" button.