Periodic tasks refactor (#62)

* Once every second the session run a list of periodic tasks on every
instance concurrently. We use these tasks to do things like:
- Collect mem and cpu stats
- Check if instance is part of a swarm cluster
- Broadcast information to connected clients

services/broadcast_info_task.go

@@ -0,0 +1,8 @@
+package services
+
+type broadcastInfoTask struct {
+}
+
+func (c *broadcastInfoTask) Run(i *Instance) {
+	wsServer.BroadcastTo(i.session.Id, "instance stats", i.Name, i.Mem, i.Cpu, i.IsManager)
+}