Graceful shutdown - defaults for io.ebean.Database to shutdown() last

[rbygrave]

For graceful shutdown, we desire components to shutdown in an appropriate order. For io.ebean.Database it should be shutdown last.

Adds a default shutdown method and shutdown priority for special components such that they default to doing "the right thing" wrt graceful shutdown.

For ebean:

  @Bean
  Database database()

We desire that to effectively default to:

  @Bean(destroyMethod = "shutdown", destroyPriority = Integer.MAX_VALUE)
  Database database()

... we want the generated code to have addPreDestroy() like:

var bean = factory.database(builder.get(ConfigWrapper.class,"!config"));
var $bean = builder.register(bean);
builder.addPreDestroy($bean::shutdown, 2147483647);