Update spring-boot-versions to generate a dependency-tree file and
attach it as an artifact. The file is generated by creating a temporary
POM and calling the invoker plugin.
The spring-boot-versions POM now depends on all spring-boot-starter-*
POMs to ensure that they have been installed before the dependency
tree is processes.
See gh-1047
Add a new maven project containing a versions.properties file and
an effective POM. Rework existing projects to use the versions
artifacts.
Partially reverts 307fbba9e4
Fixes gh-913
Spring Buildmaster
Phillip Webb
Andy Wilkinson