Simplify the exclusion logic used in Gradle by implementing implicit
exclusions rather than trying to detect transitive excludes.
This commit reverts much of the code originally included to fix gh-1047
which adds far too much complexity to the build and still doesn't solve
the underlying issue.
Fixes gh-1103
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
