jackson-databind: Add PackageVersion to improve Android memory usage

This builds on the support in
https://github.com/FasterXML/jackson-core/pull/49 to improve Android
memory usage for apps that use jackson-databind.
Update PackageVersion.java.in to implement Versioned.
Refactor shared properties and plugin logic into oss-parent.

Revert changes to .gitignore, now that generated sources are under target/ dir.
Add a unit test.
Merge pull request #139 from bgertzfield/master

jackson-databind: Add PackageVersion to improve Android memory usage