Issue #8 - Add MongoDB Text Search Sample

The sample reads the spring.io/blog atom feed and performs text search on it.

We use
- manual index creation and query via MongoTemplate
- automatic index creation and derived queries via Repository
#8 - Some polishing of the sample.

Introduced the usage of Lombok to be able to get rid off the getters and setters. Simplified the configuration to use Spring Boot's auto-configuration. The initializer is now an enum manually triggered with a MongoOperations instance. Switched from MongoTemplate to MongoOperations where possible. Polished some JavaDoc.