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This reverts commit 69985bb1.

ParallelTTracker. Particle-Matter interaction doesn't work either at the moment.

I hope that I didn't create too much of a mess when merging!

moving Classic into src directory and pack all objects into libOpal since Classic also depends on libOpal

- remove 'using namespace' from header files
- remove 'using std::string' and 'using std::abs' from header files

For reason see:
o http://stackoverflow.com/questions/5849457/using-namespace-in-c-headers