Support dependencySet of Spring Dependency management plugin

[usr42]

With this change also dependencySet notations of the Spring Dependency management plugin is supported.

Example:

dependencyManagement {
    dependencies {
        dependencySet(group: 'org.hibernate', version: hibernateValidatorVersion) {
            entry 'hibernate-validator'
            entry 'hibernate-core'
        }
    }
}

[patrikerdes]

LGTM, thanks for your contribution 👍