plot_pie_sum raises ValueError: too many values to unpack (expected 4) on every call

[ivankrylov]

src/graphing/plotting.py:101 unpacks 4 return values from filter_and_group, but that
function returns 5 (timestamp_groups, datapoint_groups, group_labels, colors,
alphas — see src/filter_and_group.py:52). Every other caller in plotting.py
correctly uses ..., colors, _ =.

Any call to plot_pie_sum fails immediately:
ValueError: too many values to unpack (expected 4)