Try enable node execution debugging with running their code in different AppDomains

Currently each `NodeRunner` runs it's node in separate process. This provides good isolation, but does not allow to debug specs with break points, etc. Only debugging via test output is possible.

That would be cool to be able to run specs from VS, and set breakpoints for debugging. This is possible if running nodes in same test process, but different AppDomains - this is basically what xunit runner does for parallel test runs.

Should give it a try.

Start by reading the NodeRunner implementation and comparing its process isolation with how the xunit runner uses separate AppDomains. The work is complete when specs can run from Visual Studio in the test process with nodes isolated in different AppDomains and breakpoints can be hit.

Written by the indexing model from the issue text.