Add route.Leader.

This class is to manipulate routing table. Curator LeaderSelector
ensures only one leader works.

If Leader takes leadership, it monitors `workers-path' and
updates router table when worker is added or removed.
Implement RoutingTableWorker

Worker uses Curator to sync consistent hashing routing table.

Worker creates sequential ephemeral node at `workers-path' with
protection mode when it starts. Protection mode add prefix with client
id to ensure that node is created.

Worker watchs `routing-table-path' and updates RoutingTable when
`routing-table-path' node is changed.

`workers-path' and `routing-table-path' is in application.conf.