Feature request: Update sankey diagrams to be more refined

[dtgaebe]

Feature description.
Update the Sankey plotting in wecopttool.utilities to have the option to plot the optimal reference average power and the deficits to it as in
rgcoe/wec_as_multiport@280464d

This results in a Sankey diagram like this:

Versus this:

[dtgaebe]

The individual quantities are calculated like this: