Currently, if we point the GUI at a .NET Core or .NET Standard assembly, we get a message saying the file couldn't be found at best and in the worst case the tree node for the assembly has a blank or empty name.

Actually running .NET Core tests is where we want to go, but that's a big job. For the moment, I'd like us to detect that the assembly is non-runnable by us and say so. Ideally, we should be able to identify the actual platform requested, e.g. .NET Core 2.1.