Polish
Update "banner" reference documentation

Fixes gh-2103
Update SpringBootServletInitializer ref docs

Add a hint to show that the `configure` method is now optional.

Fixes gh-2074
Update "logging" reference documentation

Update the logging section to reflect changes in Spring Boot 1.2

Fixes gh-1790
Update HealthInformation reference documentation

Clean and align with changes in Spring Boot 1.2

Fixes gh-2104
Drop Cloudbees PaaS documentation

Remove the Cloudbees section since they are shutting down their PaaS.

Fixes gh-2105
Update reference documentation for Spring Boot 1.2

Various updates and polish to prepare the reference documentation for
Spring Boot 1.2.

Fixes gh-1903