Implementation/Testing/Code Review: Convert GenerateRunner into maven plugin

domain-model-runtime ships with the complete domain-models-interface-extensions submodule that contains the GenerateRunner class to generate Java files from RAML files.

We need this at compile time only.

The clean solution is a maven plugin, for example rmb-maven-plugin, that runs at compile time, and will not be included into the runtime artifact.

The RAML generating code is based on a library that uses Guava 19 that has a security vulnerability () and the library breaks for fixed Guava versions.
By moving the generating code into a maven plugin that runs a compile time only we can avoid to ship the runtime with vulnerable Guava.