FORGE-1692 Probable fix.

This is probably not the right way to fix this though.
Freemarker tends to construct paths for included templates, by
manipulating the URL/path associated with the base template.

It therefore does not rely in the Resources API of Forge
beyond the base template and the ResourceTemplateLoader, thus
leaving us in a scenario where the ResourceTemplateLoader
receives a URL with a JAR scheme for classloader loaded
templates, and (possibly) URLs with a file scheme for filesystem
loaded templates.

We should probably use Resource.getName() to determine what
Resource instance to create, instead of invoking
ResourceTemplateLoader.register().