Make `HOME_NODE` a `const Core` in Grappa::impl namespace.
Make `HOME_NODE` a `const Core` in Grappa::impl namespace.

alexfrolov/grappa,alexfrolov/grappa,uwsampa/grappa,alexfrolov/grappa,buaasun/grappa,uwsampa/grappa,buaasun/grappa,alexfrolov/grappa,uwsampa/grappa,uwsampa/grappa,alexfrolov/grappa,uwsampa/grappa,buaasun/grappa,uwsampa/grappa,buaasun/grappa,uwsampa/grappa,alexfrolov/grappa,buaasun/grappa,buaasun/grappa,alexfrolov/grappa,buaasun/grappa