Added Sonatype parent POM and <scm> section.
Added Sonatype parent POM and <scm> section.

These will be needed to perform a release to Sonatype and thence on to Maven
Central.

ruslansennov/playn,threerings/playn,threerings/playn,threerings/playn,ruslansennov/playn,ruslansennov/playn,threerings/playn