Slicer inspector

[nvaytet]

Combining the range slicer with the inspector plot:

%matplotlib widget
import plopp as pp
from plopp.data.examples import clusters3d

N = 256
da = clusters3d(nclusters=500, seed=12).hist(z=N, y=N, x=N)
pp.inspector(da, dim='z', mode='rectangle', logc=True)

Fixes scipp/ess#15