[wix-devs] WIP 6108: .NET Core SCD-style BA

[Sean Hall]

I created a WIP for an initial version of a .NET Core BA. The WIP pull
request is at https://github.com/wixtoolset/web/pull/39 and the code pull
request is at https://github.com/wixtoolset/Bal.wixext/pull/8. Feedback is
appreciated.