Port away from deprecated QXmlSimpleReader

@buschinski Can you tell whether UPnP router detection works with Konversation master? Somehow the broadcast call seems to not get a respond from my router (which I had configured to be visible as UPnP device, by what the provider's device web UI allows me to do). I have not yet looked closer at things, also not compared 1.7 branch, sadly is my UPnP experience 10 years away (https://frinring.wordpress.com/2010/07/27/first-release-of-cagibi-prototype-of-cacheproxy-daemon-for-upnp-device-listening-and-publishing/),

So this patch is untested currently and was written blindly WRT real world.

Update: Meanwhile mastered modern firewall settings and made Konversation be able to reach my router, and can confirm parsing works as it should here with the (fixed) patch

@stikonas You might want to take a look at this port as well, given libktorrent has a copy of this parser code at https://invent.kde.org/network/libktorrent/-/blob/master/src/upnp/upnpdescriptionparser.cpp