determine online/offline status from local copy of close_node_changes

any node being out of the close node range considered as offline

1) currently routing::Parameters::closest_nodes_size = 16, 
2) https://github.com/maidsafe/MaidSafe-Vault/blob/next/docs/data_manager_account.md : "... If a record now contains more than EIGHT nodes the NINTH node shall be downranked and a delete message sent to the storage_node_manager of that node."

a) Given (1), IMO the code does not implement (2).
b) why is the first node is chosen to be remove?