channel_profile.analyze_channel_network_and_plot

plot.channel_profile now has function
analyze_channel_network_and_plot(), which rolls together the other
three functions in this file. This allows one-line plotting.

It should also now be possible to specify which starting nodes you
want, rather than just finding those with highest discharge (though not
formally tested). This could be useful in preventing the component from
jumping to a new channel if it manages to get bigger.