Generic service type handler for kompose

Moved label handling code from Transformer to loader,
to make it generic to handle creating service types.

Added new attribute to ServiceConfig which gets populated
in loader.

Fixes #273

pkg/kobject/kobject.go

@@ -143,6 +143,7 @@ type ServiceConfig struct {
 	Restart       string
 	User          string
 	VolumesFrom   []string
+	ServiceType   string
 }
 
 // EnvVar holds the environment variable struct of a container