Implement last missing REST API calls

[majst01]

from api.go:

// force a raft log compaction
self.registerEndpoint(p, "post", "/raft/force_compaction", self.forceRaftCompaction)

// fetch current list of available interfaces
self.registerEndpoint(p, "get", "/interfaces", self.listInterfaces)

// cluster config endpoints
self.registerEndpoint(p, "get", "/cluster/servers", self.listServers)
self.registerEndpoint(p, "post", "/cluster/shards", self.createShard)
self.registerEndpoint(p, "get", "/cluster/shards", self.getShards)
self.registerEndpoint(p, "del", "/cluster/shards/:id", self.dropShard)

// return whether the cluster is in sync or not
self.registerEndpoint(p, "get", "/sync", self.isInSync)