Update plugin, docs and sample app to Play 2.3.2

I noticed that a recent update by @edofic bumped the Play version to 2.3.1, but the sample app was still based on 2.2.0, and the README didn't have an example of how to add project settings in Play 2.3.x. (It's changed a bit since 2.2.x.) While I was fixing that, I also updated the Play version to 2.3.2.

If you accept this pull request, could you please push a new version (1.5.0?) to the Sonatype repository? That would be awesome! Thanks so much.