Add spring-boot-versions project

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-boot-tools/spring-boot-dependency-tools/src/main/java/org/springframework/boot/dependency/tools/PomManagedDependencies.java

@@ -45,7 +45,6 @@ public class PomManagedDependencies extends AbstractManagedDependencies {
 	public PomManagedDependencies(InputStream effectivePomInputStream) {
 		try {
 			Document effectivePom = readDocument(effectivePomInputStream);
-
 			for (Dependency dependency : readDependencies(effectivePom)) {
 				add(new ArtifactAndGroupId(dependency), dependency);
 			}