Feature/composableconfiguration

Hi,

I propose the following changes to export the container and it's parts catalog for use e.g in other Dependency Resolvers (I am personally using it for ShortBus, and am looking to perhaps use it also in a SignalR dependency resolver).

Ideally though, I believe we should be able to setup composable parts in consuming libraries/apps instead.
Perhaps it could be a good idea to extend the WebApplicationCatalog or create some other mechanism for this.

PS big thanks for this elegant scope solution for MEF for MVC, been looking for a while and was about to roll my own until I came across yours :) Kinda couldn't believe only WebApi has built-in support for scopes...