Gradle plugin for RAML JAX-RS code generation

This pull request contains a Gradle plugin for RAML JAX-RS code generation.  It is modeled after the Maven plugin in terms of configuration options and logic.  The included README contains information on usage and configuration.  I have also added Gradle build scripts to the Jersey sample application, which can be used to test the plugin.  The plugin itself still needs to have a Gradle task added to support the publishing of the built artifact to a remote Maven repository.  To try this all out:
* `cd gradle-plugin`
* `./gradlew build install`
* `cd ../jersey-example`
* `./gradlew raml-generate`

It is also worth noting that there is an issue with the Gradle License plugin, so its currently set to non-strict mode and there is a comment in the `build.gradle` file of the RAML plugin.