Allow the user to disable ghost loading

[robrua]

Currently, all top-level API types are ghost loaded at the core layer (they are maximally lazy loaded, only if the data requested from the object is not already known). GhostObjects currently expose a load() method, allowing users finer grained control over when these objects load if desired, but an option to entirely disable GhostLoading is desirable.

Such a solution would probably consist of providing a convenience method in Orianna which disables the GhostObjectSource and adds a number of data layer -> core layer transformers which support the types that the GhostObjectSource supports.