Create Embedded LDAP Support Classes

[rwinch]

Currently it requires multiple beans to support embedded ldap support.

	@Bean
	UnboundIdContainer ldapContainer() {
		UnboundIdContainer container = new UnboundIdContainer("dc=springframework,dc=org",
				"classpath:users.ldif");
		container.setPort(0);
		return container;
	}

	@Bean
	DefaultSpringSecurityContextSource contextSource(UnboundIdContainer container) {
		return new DefaultSpringSecurityContextSource("ldap://localhost:" + container.getPort() + "/dc=springframework,dc=org");
	}

It would be nice to provide single builder that creates/shuts down the embedded database and creates a DefaultSpringSecurityContextSource similar to Spring's EmbeddedDatabaseBuilder.