Feature and bug fix release

* default source directory moved to .../xsd (fixes #9)
* local development (gradle install) without signing (fixes #7)
* local development (gradle build) without sonatype* properties set (fixes #6)

Refactored plugin into smaller methods

In addition sample is more complete

Converted code from java to groovy

Total rewrite based on the Antlr plugin

This makes it possible to have one package for each schema file, by
just putting this into the schema (jaxb:package). Also now there is
not any configuration needed anymore (and not possible either),
except specifying the classpath for the plugin

Also added setup to Gradle so the project can be deployed to Maven

Fixed group id (nos.entitas --> nos.entitas.gradle)

Tagging version 1.0