Make JQuantLib thread safe

[Richard Gomes]

This is a subject we need to explore more.

Making JQuantLib 100% thread safe would possibly imply on serious performance penalties.

On the other hand, there's particular concern that QuantLib/C++ is not thread safe and obviously JQuantLib would inherit the same behavior.

So, the idea would be:

1. first of all identify areas where JQuantLib is not thread safe;
2. mark all non-thread-safe classes with @NonThreadSafe
3. study critical points where thread safety is needed
4. fix the code where thread safety is needed and mark those classes with @ThreadSafe

In particular, step (1) can be easily done marking all classes with @ThreadSafe and running FindBugs.

More info:
    http://jcip.net/annotations/doc/index.html