Refactor for Maven builds

My aim was to refactor the project to be built standalone, using Maven.
No source was touched, however many files moved.
The Maven project follows the original project layout (subpaths for src may have been altered to be Maven defaults)

All IDE specific files (IntelliJ) have been deleted, and .gitignored as IntelliJ and others are able to fully import Maven projects.

This is my first public pull request, please be gentle ;)