[#70] More comprehensive dependency management - PoC

With [dependency-management-plugin](https://github.com/spring-gradle-plugins/dependency-management-plugin) from Spring. The mechanism in old good Maven style ;).

In addition the it has an ability to [import Maven bom](https://github.com/spring-gradle-plugins/dependency-management-plugin#importing-a-maven-bom) (currently not used, but useful when using the whole stack from Spring.io).

WDYF? Is it more readable for you?