Fix for jar.

A new, clean patch for missing imports, allowing creation of a viable jar. First referenced in [#67](https://github.com/hype/HYPE_Processing/issues/67), first cut at a patch in (closed) [#70](https://github.com/hype/HYPE_Processing/pull/70).
This should apply cleanly, and has been tested in the PDE in Java mode (as well as with `processing-java`, and in the PDE in Python mode. Standalone Python is experiencing some library resolving difficulties at the moment).
The `atan2` call on line 100 of HMagneticField is a horror, but it won't resolve any other way, and I can't figure out why. I am certainly open to enlightenment.