Ask support for ActorSelections (and other non-Actor types in the future)

Although Scala futures look and feel an awful lot like Tasks, I don't really understand some of their uses inside Akka itself.

One problem I needed to solve this morning is being able to wait on a Future from an ActorSelection in Pigeon. I decided that the best construct for doing this was to create an Ask extension method inside the `AskSupport` class.

https://github.com/Aaronontheweb/Pigeon/blob/edc083d690e0db1791ab16eb1a446d323bbc51f0/src/Pigeon/Actor/AskSupport.cs

I added a unit test for this to `ActorSelectionSpec` and it passes, but one issue with this code now is that the FutureActor gets registered in the /user/ space rather than in /temp/ - is there a better way of doing this?

Best,
-Aaron