Full Maven/Gradle/sbt support for Play

[gmethvin]

Lagom currently has sbt and Maven support. Play officially supports sbt, and there are third-party Maven and Gradle plugins that seem to work pretty well. Ideally I'd like to use the same thing for both Play and Lagom. It might make sense to start supporting the existing third-party plugins for Play, because they seem relatively complete.

[TimMoore]

Closing this in favor of moving it to the Play road map. It's also a rather large item and should be split up.