Upgrade to Spring Boot 2.0.0.RC1

...along with Spring Cloud Finchley.M6, and Spring Cloud Stream Elmhurst.M4

Update Spring Security policy settings as well as default dummy accounts using new APIs, and new reactive APIs.
Update custom Thymeleaf authorization processor to find SecurityContext inside the exchange. (Still no thymeleaf-extras-springsecurity5 WebFlux support)
Replace custom Spring Cloud Gateway filter with comment because code was contributed to the project.
Patch some unit tests that broke due to constructor settings for Selenium.

learning-spring-boot / learning-spring-boot-2nd-edition-code