Add support for Function and Trigger domain objects (#1060)

Vast commit, includes:

 * Introduces the Trigger domain entity.
 * Introduces the Fns domain entity.
 * V2 of the API for interacting with the new entities in swaggerv2.yml
 * Adds v2 end points for Apps to support PUT updates.
 * Rewrites the datastore level tests into a new pattern.
 * V2 routes use entity ID over name as the path parameter.

api/const.go

@@ -1,12 +1,16 @@
 package api
 
-// Request context key names
 const (
-	App   string = "app_name"
-	AppID string = "app_id"
-	Path  string = "path"
-	Call  string = "call"
-	// Short forms for API URLs
-	CApp   string = "app"
-	CRoute string = "route"
+	// Gin Request context key names
+	AppName string = "app_name"
+	AppID   string = "app_id"
+	Path    string = "path"
+
+	// Gin  URL template parameters
+	ParamAppID     string = "appId"
+	ParamAppName   string = "appName"
+	ParamRouteName string = "route"
+	ParamTriggerID string = "triggerId"
+	ParamCallID    string = "call"
+	ParamFnID      string = "fnId"
 )