Off by default.
Expand config options to show the user agent used.
Re-use this to show more useful info in Help->About too.

Change-Id: I1044116ef9beeb341a537c0f4451dca54e198f67
Reviewed-on: https://gerrit.libreoffice.org/20098Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>