Added action_plan.create|update|delete notifs

In this changeset, I added 3 notifications:

- action_plan.create
- action_plan.update
- action_plan.delete

Partially Implements: blueprint action-plan-versioned-notifications-api

Change-Id: I8821fc6f47e7486037839d81bed9e28020b02fdd

watcher/common/exception.py

@@ -174,6 +174,14 @@ class EagerlyLoadedAuditRequired(InvalidAudit):
     msg_fmt = _("Audit %(audit)s was not eagerly loaded")
 
 
+class InvalidActionPlan(Invalid):
+    msg_fmt = _("Action plan %(action_plan)s is invalid")
+
+
+class EagerlyLoadedActionPlanRequired(InvalidActionPlan):
+    msg_fmt = _("Action plan %(action_plan)s was not eagerly loaded")
+
+
 class InvalidUUID(Invalid):
     msg_fmt = _("Expected a uuid but received %(uuid)s")