Move version to gradle.properites for Artifactory release management
Update so the pom conforms to Maven Central requirements

See https://docs.sonatype.org/display/Repository/Sonatype+OSS+Maven+Repository+Usage+Guide#SonatypeOSSMavenRepositoryUsageGuide-6.CentralSyncRequirement
Merge pull request #42 from rwinch/artifactory-release

Artifactory release