Ellipsoid factor blows up if input image is bigger than Integer.MAX_VALUE pixels

[mdoube]

Describe the bug
Run Ellipsoid Factor using an image with more than Integer.MAX_VALUE pixels and it blows up because (presumably) the underlying map of starting points is a) pixelwise and b) (backed by) a 1D array rather than a 2D array (which has int × int pixel space).

Caused by: java.lang.RuntimeException: Number of elements in ArrayImg too big, use for example CellImg instead: 3445814736 > 2147483647