Porting of OBO file parser from BioJava 1 to BioJava 3

I created a new module biojava3-ontology that contains everything needed for parsing OBO files. It is a port from BioJava1 and also includes the change-event model that was part of it.  I could not easily refactor it. Not sure if anybody finds this useful. Perhaps we need to think how to take that out. As such I am not committing this directly, but submitting a pull request for discussion.

This is a fix for #33.