Add SHOW STATS_TOTALS / STATS_AVERAGES as admin commands

Add SHOW STATS_TOTALS / STATS_AVERAGES as admin commands

We already had SHOW STATS, but after adding the wait_time colums it
got a bit too wide for regular screens. That's incovenient, as the
admin interface does not selecting only some of the columns.

But in most cases we're only interested either in totals or averages,
not both at the same time. So let's add commands showing only the
relevant subset of columns.