Log Message:
Add new package liquibase

Liquibase is an open source (Apache 2.0 Licensed), database-independent
library for tracking, managing and applying database changes. It is
built on a simple premise: All database changes are stored in a human
readable, yet trackable, form and checked into source control.

Provided by mmoll in netbsd/pkgsrc pull request #6, with some changes from
myself.