Add API Reference for Watcher

This patch set adds API Reference along with some
fixes to documentation. It partially fixes bug #1757423.

Change-Id: I107b4fd5daf40aad63fc13864debbbbc82a9826c

api-ref/source/samples/actionplan-start-response.json

@@ -0,0 +1,22 @@
+{
+    "state": "PENDING",
+    "efficacy_indicators": [],
+    "strategy_uuid": "7dae0eea-9df7-42b8-bb3e-313958ff2242",
+    "global_efficacy": [],
+    "links": [
+        {
+            "rel": "self",
+            "href": "http://controller:9322/v1/action_plans/4cbc4ede-0d25-481b-b86e-998dbbd4f8bf"
+        },
+        {
+            "rel": "bookmark",
+            "href": "http://controller:9322/action_plans/4cbc4ede-0d25-481b-b86e-998dbbd4f8bf"
+        }
+    ],
+    "updated_at": "2018-04-10T11:59:41.602430+00:00",
+    "strategy_name": "dummy_with_resize",
+    "uuid": "4cbc4ede-0d25-481b-b86e-998dbbd4f8bf",
+    "audit_uuid": "7d100b05-0a86-491f-98a7-f93da19b272a",
+    "created_at": "2018-04-10T11:59:12.592729+00:00",
+    "deleted_at": null
+}