fUML.Library and fUML.Test packages are only used for builtin tests

The fUML.Library and fUML.Test packages are left over from the original generation of the execution engine code from the early execution model. However, they are now only used by the unit tests under org.modeldriven.fuml.builtin. It is therefore confusing to have them in under the src/main/java hierarchy. They should be moved under the builtin testing package.