Merge pull request #4 from Garyfallidis/quickbundles

Generalized quickbundles  tutorial
Moved Cluster and ClusterCentroid outside Cython code
If streamlines is empty return empty clustermap in quickbundle
Merge branch 'quickbundles' of github.com:MarcCote/dipy into quickbundles
Added another import in metric.py
Merge branch 'quickbundles' of github.com:Garyfallidis/dipy into quickbundles
Finished refactoring ClusterMap and cleaning the tutorial for ISMRM
Added the AXY colormap
Meeting with Elef updates