Fix the way components are loaded

[mlorbetske]

Currently components are loaded via trickery (dotnet publish on a dynamically generated project.json places the required assemblies in a path that's more or less treated as an additional probing path)

The new model operates over the packages in the package cache, but simply loops over the assembly load locations trying to load stuff until nothing more succeeds.

We should move to a model that's smart enough to automagically load things in the correct order.