Base service loading

Need code to load IpcService, UniverseManager, and any other services that need loaded.
These services are the core pieces of Do and should each be implemented for their respective platform. Common code such as Interfaces, Abstract classes, or services which don't need anything platform specific should live in Do.Services.

The services should be Mono.Addins addins.

We want to keep Do core as light as possible, so let's hold off on things like notifications and all the cruft that gets thrown in until we show they're truly needed.

A lot of this code can be taken from trunk Do Services.cs.