Feature gradle plugin

This applies the Gradle plugin.

I've built the app before applying the plugin and after and made sure that the resulting apps are the same.

I've also changed the publishing a little to put all Mule 3.4.0 apps into their own repo in Maven.  This is intended to make this process simpler when we next have to upgrade Mule.

There will be a few more pull requests like this on other Mule projects.