Update mpdroot for ROOT 6.30.x, Pythia 8.3.11, and external FFTW3
With recent changes of dependencies, build system and mpdroot's code need to be updated as well. Namely:
- ROOT starting from 6.30 has changed way how it returns version number (from 6.28/XX to 6.30.XX)
- Pythia 8.3.11 contains some major changes compared to 8.3.9, our code needs to be changed accordingly
- FFTW3 can be either in-built in ROOT or provided as external package, our linking needs to be fixed accordingly