XD-2119,XD-2143,XD-2144

* Add 'spring-boot-starter-security' as a dependency
* Set up the admininstration and management endpoints as insecure by default
* Unit tests for SSL
* Unit tests for security enablement
Good point, Ilaya. In fact we also need to include SSL/HTTPS configuration options there as well. I added https://jira.spring.io/browse/XD-2181 to capture that.