pom:xml: use <dependencyManagement> to force versions of spring-core, spring-context and spring-beans

pom:xml: use <dependencyManagement> to force versions of spring-core, spring-context and spring-beans to 3.2.x. instead of exclusions on spring-data-jpa dependency because Maven sometimes pulls both versions 3.2.x and 3.1.x versions of coring-core, spring-beans and spring-context.