REORG: stats: dump the frontend's HTML stats via a generic function

REORG: stats: dump the frontend's HTML stats via a generic function

This new function stats_dump_fields_html() checks the type of the object
being dumped from the stats table, and emits it in HTML format. It uses
an argument indicating if the HTML page is also used as an admin page,
and for now still takes the proxy in argument as a few entries still
need it.

The code was simply moved as-is to the new function. There's no
functional change.