FFD library with parallel loops. required for GH_Wind

Please refer to this publication for citation: Waibel et al. (2017)

Modified after: https://github.com/lukasbystricky/GSoC_FFD

To Do:

• bug: pressure field keeps updating in an open domain
• add energy transportation (Boussinesque approximation)
• add pollution transportation (Fick's law)
• add numeric convergence indicators
• try different PDE solvers (multigrid, conjugate gradient, TDMA...?)
  
  
• parallelize on GPU
  
  
• meta models for spatially resolved effective viscosity