More fullnode -> validator renaming (#4414)

* s/fullnode_config/validator_config/g

* s/FullnodeConfig/ValidatorConfig/g

* mv core/lib/fullnode.rs core/lib/validator.rs

* s/Fullnode/Validator/g

* Add replicator-x.sh

* Rename fullnode.md to validator.md

* cargo fmt

multinode-demo/replicator-x.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+#
+# Start a dynamically-configured replicator
+#
+
+here=$(dirname "$0")
+exec "$here"/replicator.sh --label x$$ "$@"