#14 - Upgraded to Spring Boot 1.2.

We now use the Maven property java.version to define the Java version instead of declaring the compiler plugin manually. Use Spring Boot's logging properties instead of a dedicated Logback config file.

Some minor code polish in GuestbookEntry (use final fields where possible).
#15 - Upgraded to Thymeleaf 2.1.4.

We're now able to remove the component name customization from Guestbook as Thymeleaf 2.1.4 does not accidentally pick up the bean anymore.