mod_status: Add cumulated response duration time

in milliseconds to auto mode.

Partial backport of r1839532 from trunk
(only auto mode changes, html parts not yet
backported).

Submitted by: rjung
Reviewed by: rjung, jim, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1839533 13f79535-47bb-0310-9956-ffa450edef68