Fix the signature and add deprecation warnings for optimize_* methods.
`plot_exchanges_per_taxon` will now use normalized fluxes (per 1 gDW for each taxon)
which allows better comparability. The old behavior can be enabled with
`use_total_flux=True`.
Avoid negative growth rate constraints in `_apply_min_growth`.
Can now enable presolving/scaling in `grow` and `tradeoff`.