Add Time Trigger API and client (#153) (#161)

This change adds a timer trigger API, client, and implementation.  Users can trigger a function with a cron-compatible string. 

This change also moves the publisher interface and webhook-based publisher implementation out of kubewatcher and into a separate `publisher` package.

timer/main.go

@@ -0,0 +1,30 @@
+/*
+Copyright 2017 The Fission Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package timer
+
+import (
+	controllerClient "github.com/fission/fission/controller/client"
+	"github.com/fission/fission/publisher"
+)
+
+func Start(controllerUrl string, routerUrl string) error {
+	controller := controllerClient.MakeClient(controllerUrl)
+	poster := publisher.MakeWebhookPublisher(routerUrl)
+	MakeTimerSync(controller, MakeTimer(poster))
+
+	return nil
+}