Started working on ellipsoid visualization
Added tensor function for tensor visualization as ellipsoids
Removed show from test
Added option to visualize the odfs with the color_fa color
Updated suggestions and examples
minor changes

modified:   ../dipy/tracking/eudx.py
modified:   ../dipy/tracking/propspeed.pyx
modified:   examples/reconst_dti.py
modified:   examples/segment_quickbundles.py
Added clipping of odf in csa
Made fvtk.tensor more flexible. It can now colour with different scalar fields like the color_fa
TEST+DOC in ellipsoid and docs

Added tests for number of actors

modified:   ../dipy/viz/fvtk.py
modified:   ../dipy/viz/tests/test_fvtk.py

Added docs for color_fa normalization of the ellipsoids
and clipping of the csaofs to be positive

modified:   examples/reconst_csa.py
modified:   examples/reconst_dti.py
Merge pull request #212 from Garyfallidis/fvtk_ellipsoid

NF+BF - Tensor visualization.