New module layout required

[FroMage]

So, if we add this APT processor in the classpath, we pull in all our deps in the user's classpath, including Groovy and our specific version of Hibernate.

In Maven, we can specify an APT processor module as part of the compiler plugin config (see https://maven.apache.org/plugins/maven-compiler-plugin/compile-mojo.html#annotationProcessorPaths) which doesn't add it to the user's classpath, which is probably cleaner.

But it also means the user won't have the @CheckSQL annotation in his classpath. So if we want to support that use-case, we'd need to extract the annotation to its own module.