Finish CDS work

[mhalbritter]

Open points:

• Fix documentation (blocked until Phil is done with the doc work)
  • layers.enabled and layers.includeLayerTools
  • spring-boot-jarmode-layertools has been renamed to spring-boot-jarmode-tools
• Add note to release notes that layers.enabled = false no longer prevents the inclusion of the spring-boot-jarmode-layertools JAR
• Update "Unpacking the Executable JAR" to use the new extract command instead of fiddling with the JarLauncher or constructing the classpath yourself.