[Spring Boot] Added embedded FabricSpringApplication

Sometimes users may like to embed our Fabric application into existing Spring context (for example to use `io.fabric8.process.spring.boot.container.web` system property is all Fabric-managed jar processes). `EmbeddedFabricSpringApplication` can be easily added as a bean to existing Spring contexts (with one-liner bean definition) and it will automatically start Fabric Spring Boot as a child context.