ENH:  grow labels in parcellation
API:  integrate growing labels without over lap into grow_labels
TEST grow_labels without overlap (BK)
FIX grow_labels(overlap=False):  assign each vertex to closest seed
ENH grow_labels:  Allow seeds with multiple vertices.
ENH grow_labels:  add label names, `names` parameter
FIX grow_labels:  variable name conflict
FIX grow_labels():  assign color to each label
Merge pull request #1165 from christianmbrodbeck/grow-parc

ENH:  grow labels in parcellation