Add Router pool support

[rogeralsing]

We need to add router pool, e.g. RandomPool, RoundRobinPool

[Aaronontheweb]

Before I can really scale out my service I'm building on top of Pigeon, I am going to need:

• Consistent hash routing
• Being able to mix remote / local actors into a single router
• Pool-based routing

So I'll be chipping away at these once those issues come to a head in my own project, which will be soon

[rogeralsing]

Prepping a bit on this one.
Apparently routing support was rewritten very recently so the current Pigeon impl is not up to date with the current Akka impl

[Aaronontheweb]

Starting work on this - added support to view the number of messages currently inside a mailbox (among other things) yesterday. Going to work on this over the next few days.

[rogeralsing]

I've refactored some stuff in the router support, I Think I will have non-resizable pools up and running later today..

[Aaronontheweb]

Just pushed some commits that should mark the initial RoundRobinPoolRouter implementation as complete. Going to do some cleanup and stub out some of the code for resizeable pool routers before I mark this issue as closed.

[rtumaykin]

Started working on the resizeable pool router implementation.

[rogeralsing]

I did some changes in the ActorRefProvider for this, the provider now creates the correct type of cell for the resizable pool routers, and RouterManagementMessages can be sent to the router instead of the routees.

Hope I didn't interfere with @rtumaykin's work

[rogeralsing]

This is completed IMO, closing