Topics and People link to a list of all of them.

At the top of any person or topic page, there is a line that says

    SelectedPapers.net > People > Name

or

    SelectedPapers.net > Topic Group > Topic

This PR makes "People" and "Topic Group" link to an index of all people or all topics (by doing a search for ".").

It's not as pretty as it could be, but having easy access to an index of everybody/everything is useful.  Yes, you get a long list of results, but you can then use your browser's find function to find any user, check whether a given person is using spnet, or check whether anybody is using a tag with "numerical" somewhere in it that you're not aware of (for instance).