Implement outgoing webhooks.

model/config.go

@@ -29,6 +29,7 @@ type ServiceSettings struct {
 	GoogleDeveloperKey         string
 	EnableOAuthServiceProvider bool
 	EnableIncomingWebhooks     bool
+	EnableOutgoingWebhooks     bool
 	EnablePostUsernameOverride bool
 	EnablePostIconOverride     bool
 	EnableTesting              bool