Componentize parts of VT

[lifflander]

What Needs to be Done?

The high-level idea is to create separate components for useful pieces like the location manager or load balancing framework that are not reliant on the rest of the system to function. They will still require the user to implement some send/recv and perhaps even higher level concept like termination detection, but with that in hand the user can use the component. We may even provide default implementations for this that relies purely on MPI.

I think the first target will be load balancing, specifically a TemperedLB implementation is that separated from VT.