added PomFile abstraction
maven exclusions actually require both artifactId and groupId so updating plugin to add a '*' exclusion if either group or module is null for the exclusion
Merge pull request #31 from mlueders/add_pom_file_abstraction

added PomFile abstraction
Merge pull request #32 from mlueders/fix_maven_publish_ext_exclusions

Fix maven publish ext exclusions
[Gradle Release Plugin] - pre tag commit:  '0.14'.
[Gradle Release Plugin] - new version commit:  '0.15-SNAPSHOT'.