Updates for microbial oil production

[yoelcortes]

Hi @yalinli2.

The main change of this pull request that you should be aware is:

• The specification for the imbibition water for the juicing system. Now the oil is treated the same as the rest of the dry biomass because most of the oil is retained within the bagasse. The imbibition water requirement now does not change with lipid content (but does change with cane moisture content). Previously, high lipid content meant unreasonably low imbibition water requirements.
• A fallback in the specification for glycerol purification was introduced to avoid infeasible regions (all results the same).

Note that all biorefinery tests remained the same except for oilcane biorefineries, which changed only slightly (I would even say negligible).

Other changes are related to microbial oil production and documentation for biosteam's readthedocs. No changes in stream connections were made.

Thanks,

[yalinli2]

Thanks @yoelcortes! Somehow this PR slipped through my notice, I'm good with merging it in!

[yalinli2]

Oh and btw the WWT paper is out so I'm less concerned about changes in the other biorefineries (as long as there are no significant changes in the metrics and all tests can pass)