Added experimental file for filtering streamlines
Added two new files : fvtk_actors.py and fvtk_util.py, for streamlines visualization with vtk
Merge pull request #22 from StongeEtienne/new_fvtk

New fvtk streamlines visualization
Merge branch 'new_fvtk' of github.com:Garyfallidis/dipy into new_fvtk
New file for vtkWidgets addes slide_widget function
Adding button widget still work in progress
Updated filter_streamlines still wip
New file named guillotine added
Implemented a working slicer
Refactored guillotine in a class
Added Numpy -> vtkImageData conversion
Changed add_data_volume default opacity
Corrected axis orientation for image space visualization