qdoc3: Added scope attr to https and mailto links.
qdoc3: Added scope attr to https and mailto links.

In DITA XML, these links now have scope="external".

Task-number:  QTBUG-23940
Change-Id: Iae241d218b6377400aaa3dde6ddae208b0756132
Sanity-Review: Qt Sanity Bot <5581206bb7e0307f0d99eb71898ae6b694149ca5@ovi.com>
Reviewed-by: Gary Aish <b4d1444d9f14692e1904b093a1259fe0c22593a7@nokia.com>
Reviewed-by: Martin Smith <a8cc6484db2755056ccf1c457da8ca771f895dea@nokia.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc