Use Spring Resource Instead of File for Factory Beans

[Tom Zeller]

> The only reason this is open at all is the dependency issue. If we build
> the MetadataResolver on top of Spring Resources, then the whole opensaml
> package ends up with a Spring dependency. If Spring Resources were in
> their own jar, I suspect we'd be much more happy to do it.
>
> I don't suppose they factored that out in 4.0, which I see is almost done?

Spring Resources as of 4.0.0.M3 are still in spring-core, fwiw.