Change scope->environment and namePrefix->appName

[rkuris]

It's all through the code, and it's still to hard to explain. These terms are more easily understood.

While we're making this change, we should also add the appName (formerly namePrefix) to the CreateEnvironment (formerly CreateScope) call to improve our ability to route and/or name keyspaces based on both.

[eculver]

We should just push forward with this refactor as a part of the scope lifecycle work I have planned. I think we should start publishing our internal RFCs to make this more transparent.

TODO(eculver)