make BalancingLearner work with the live_plot

The following would need to work:

dmap = hv.DynamicMap(lambda X, Y: hv.Scatter([(X,Y)]), kdims=['X', 'Y']).redim.values(X=[0, 1, 2], Y=[2, 3, 4])
hv.HoloMap(dmap[:, :])

Depends on https://github.com/ioam/holoviews/issues/3085.