fixed player crash when accessing unknown custom field i.e. the one that has not been stored in the CC3D settings
fixed player's rendering of vector field in 2D on hex lattice
added VTK function wrapper which releases GIL - necessary if one wants to do non-blocking VTK data point reads using VTK provided functions. The trick was to write requested functionaluity in C++ and then wrap this function usign SWIG with threads=1 option enabled in SWIG
Cleaned up player code a bit. Improved VTK file replay in the Player. The code related to this task is much simpler, cleaner and more responsive because reading of VTK files is non blocking. Should work fin on OSX...