Added Spring Boot auto-configuration support.

This commit adds Spring Boot style auto configuration. With this change, an app using `spring-boot-cf-service-broker` can use `@EnableAutoConfiguration` to enable component scanning of `spring-boot-cf-service-broker` components without having to add a `@ComponentScan` annotation containing the `spring-boot-cf-service-broker` package. 

This also eliminates the need to exclude beans like `BrokerApiVersionConfig` and `BeanCatalogService` when the app wants to override with their own behavior. `spring-boot-cf-service-broker` will provide default versions of these beans if the app doesn't provide one, or back off if the app does provide its own beans.