Fixing outdated sonarqube and adding dotnet core tests

[potatman]

No description provided.

[igitur]

Why are you removing the net452 target?

[potatman]

Because netstandard1.2 can be used by net4.5.1 and above, so it is redundant. https://docs.microsoft.com/en-us/dotnet/standard/net-standard

[igitur]

I think you guys were a bit quick to just drop a target framework. We were explicitly supporting older versions of Visual Studio through the QLNetOld.sln and QLNet.Old.csproj files. That project relies on a net452 build. If we drop .NET Framework support, that means people who build QLNet themselves will require a later version of Visual Studio and hence we can drop the "old" .sln and .csproj files. At the moment we're sitting with a half-baked implementation.

So do we want to support older version of Visual Studio (and then also .NET 4.5.2) or do we decide that every developer should be on a later (I think 2017+) version of Visual Studio?