Just some line-wrapping to make this code nicer to read.
RF: Add an 'origin' argument to sphere_funcs.

This allows moving the sphere_funcs from their current (0, 0, 0) position to
other positions in space, allowing using this together with a volume actor,
showing (for example) the b0 image.
BF: What's the point of using the fvtk.camera function if you reset it here?
NF + BF: Add origin argument to `peaks`. Fix bugs with handling multi-d data.