Download postgresql-test-datasource JAR file with all dependencies

An integration test helper designed for dk.kosmisk:postgresql-maven-plugin. It is able to create a DataSource that connects to a postgresql, given a system-property with a port in it and a database name, or a URI in an environment variable or from PG* environment variables or to a personal PostgreSQL instance, with user/password/database-name which is the same as the user name for the user running the tests.