Separate pbinary from from_labels()

[hughesadam87]

Maybe it's too much work, but it's confusing to have pbinary keyword, since we are talking about two distinct tasks in labeling from a background. I still think this should be a canvas method. Maybe an alternative is that if 0 particles are found, a warning is raised that reminds us of this facet? And on top of that, there's still this bug with pmin < 10 to handle..