Add minimal setup for Native Packager

[ches]

Play includes SBT Native Packager, but it won't work without at least some minimal metadata filled in the build configuration. This adds enough to produce a working Debian package with the debian:packageBin task. The universal:packageBin task should also work to produce a zipball containing built jars and run scripts.

Upgraded to Play 2.3 because from what I could tell, the version of Native Packager in 2.2 did not support the Java Server Application archetype, the desirable way to deploy a utility service like this which is the default in Play 2.3 settings. This required adding the sbt-less plugin since asset stuff has now been modularized.