Theme engine: fix resource dependencies in nxthemes-lib / broken theme editor

The resource servlet (nxthemes-lib/...) since 5.4.3 tries to resolve resource dependencies on-the-fly but this does not work because the servlet can only serve the same type of resources, for instance if a js resource depends on a .css resource, the css resource must be served on a separate servlet. This is what currently breaks the theme editor.

It is too late to resolve resource dependencies in nxthemes-lib, which means that resource dependencies must be handled earlier in the resource registration process, this is where the bug is, i.e. some resources are contributed but the dependency graph is not updated correctly.