Rewrite Requester to be tell-based rather than ask-based?

Summary: This post points out the fragility of using "ask" too much. I suspect it'll eventually become an issue for us -- while we don't often use ask explicitly, we do use it under the hood of Requester, and we use that a lot. Also, we use ask to go from the Play layer to the middle layer.

The first step of addressing this may be a rethink of Requester. Is it possible to tweak this to not be ask-based, or to ameliorate the timeout problems of ask? How could we make this work better? Could we detect the sort of timeout problems listed here? Could we print better stack traces automatically?