Extractor expansion

Hi, Julian (@jboelhau) and I were supervising Joshua Friedman, a summer student. As we were planning to develop multiple rivet plugins and HEPData entries, we were asked by @agrecu if we could also test the HEPData extractor. During our testing we realised that the HEPDataExtractor in its current state did not support some of the table formats we were working with, so we asked our summer student to extend this tool. This resulted in a rewrite of this project, which was then later reviewed by Julian and me. With the changes we propose, the new version of the HEPData extractor can automatically parse many different table-types and could be extended a bit more in the future. Feel free to have a look and share your thoughts.