Move PackageVersion.java pom.xml logic into oss-parent

This refactors out the pom.xml logic to generate PackageVersion.java out of the following pull requests and into oss-parent:

https://github.com/FasterXML/jackson-core/pull/49
https://github.com/FasterXML/jackson-databind/pull/139
https://github.com/FasterXML/jackson-datatype-guava/pull/16

I also moved the generated file out of src/ and into target/generated-sources/ .