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/server/server_options.go

@@ -57,7 +57,7 @@ func limitRequestBody(max int64) func(c *gin.Context) {
 		if cl > max {
 			// try to deny this quickly, instead of just letting it get lopped off
 
-			handleErrorResponse(c, errTooBig{cl, max})
+			handleV1ErrorResponse(c, errTooBig{cl, max})
 			c.Abort()
 			return
 		}