Rename Slave to Host

The role of a slave as a host for Factorio servers is not well reflected
in its name and has caused confusion among users.  Rename slave to host
to better reflect its role as a host of Factorio servers.

docker-compose.yml

@@ -4,6 +4,6 @@ services:
   controller:
     build: .
     command: npx clusteriocontroller run
-  slave:
+  host:
     build: .
-    command: npx clusterioslave run
+    command: npx clusteriohost run