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.

fission.yaml

@@ -104,6 +104,25 @@ spec:
         command: ["/fission-bundle"]
         args: ["--kubewatcher"]
 
+---
+apiVersion: extensions/v1beta1
+kind: Deployment
+metadata:
+  name: timer
+  namespace: fission
+spec:
+  replicas: 1
+  template:
+    metadata:
+      labels:
+        svc: timer
+    spec:
+      containers:
+      - name: timer
+        image: fission/fission-bundle:alpha20170124
+        command: ["/fission-bundle"]
+        args: ["--timer"]
+
 ---
 apiVersion: v1
 kind: Service