Wip/cleanup for play

* Add the formal bash/bat script generation to the JavaApp archetype
* Cleanup the JavaApp archetype settings + documentation so it's *one* definition for the simplest projects
* Add tests to ensure that vanilla `dist` and `stage` in the sbt prompt work
* Add tests for the JavaApp archetype
* Cleanup the script templating in the JavaApp archetype.


Review by @huntc with the following notes/caveats:

1. `make-bash-script` and `make-bat-script` return `Option[File]` rather than `File`.  This means we could default to None if we had to.  Right now `JavaApp` archetype would be ok either way.  I'm on the fence as to how we should actually do this.  You'll have to use the java app archetype settings to get these defaults though, which I *think* is the right thing for play right now.
2. The `bat` file remains untested until I pass this code off to the windows box.  Wanted to get this in font of your eyes, as I'll be on windows the rest of the day.
3. You may have to manually specify `mainClass` in play, unless it already does this.

Let me know what you think.