DOC: added slice of gfa together with odfs
RF: cleanup of slicer
NF: added simple camera setter function
BF: A possible bug fix for vtk6's for rendering large images
DOC: typo corrected
BF: outline now works
Merge pull request #251 from Garyfallidis/slicer_odfs_together

Another cleanup for fvtk. This time the slicer function was simplified