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
https://github.com/rgcoe/wec_as_multiport/commit/280464de5242d0372f815c4a1d4a83a0d41aa183

This results in a Sankey diagram like this:

Versus this:

[dtgaebe]

The individual quantities are calculated like this: