Debugger id

I'm a little confused about the plan going forward- this is a new debugger with a different debug adapter id, debugpy. I understand that the "python" debug adapter will be deleted from the vscode-python extension. But what about previously existing "python"-type launch configs?

Also, I think that "python" works better as a debug adapter type than "debugpy" for the same reasons I described in #42, it just makes more sense to the user, I think.