"Last updated" on place detail page should show last analysis job date

[KlaasH]

The "Last updated" text on the places list shows the date that the most recent analysis (i.e. the one shown) was run.

But the "Last updated" date on the place detail page shows the most recent change to the Neighborhood object itself. Usually those are the same, since the Neighborhood gets updated when the analysis runs and not otherwise. But not always--when I changed Minneapolis from "hidden" to "public" (issue #740), that caused its modified date to change, and the date of that change started showing on the detail page.

I think we always want "Last updated" to be the date of the last analysis.