InternalKnowledgeBuilder.Empty should delegate all the methods

InternalKnowledgeBuilder.Empty should delegate all methods to real impl because it is possible to build an empty project and then incrementally add resources (this is what BC normally does)

https://github.com/kiegroup/drools/blob/master/drools-compiler/src/main/java/org/drools/compiler/builder/InternalKnowledgeBuilder.java#L92