Weld SE bootstrap API - allow to register additional org.jboss.weld.bootstrap.api.Service implementations

Right now, a service may be registered using the ServiceLoader mechanism (see also http://docs.jboss.org/weld/reference/latest/en-US/html/ri-spi.html#_registering_services) or the org.jboss.weld.environment.se.Weld.createDeployment() method must be overriden.