Enhanced project structure

The current project structure does not support the future development as well as an integration of GERBIL into the [HOBBIT platform](http://project-hobbit.eu/) because it has several drawbacks:
- All classes are located in one single project that aims at building a war file. This makes it hard to
- reuse parts of GERBIL and
- develope additional experiment types, e.g., QA.
- Important modules that are not part of the main project, i.e., the nif.transfer library and the NIF-based webservice that is used for testing, are managed in different branches. However, they should be managed as modules.

Thus, we would like to move from the current project structure to a maven multi module project comprising modules for a parent pom, basic data classes, evaluation classes, experiment classes, nif-related classes, web services (NER/NEL and QA).