Update MCT Documentation

[hannahlanzrath]

Fixes Issue #223

Throughout this PR we've also found and fixed some issues with the radial flow documentation, and updated the MCT interface so that NCHANNEL is not a discretization but model parameter. These changes will be put in separate commits.

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[hannahlanzrath]

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[hannahlanzrath]

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[hannahlanzrath]

Mind that

Fix spelling Mistake within Radial Flow Model (found by accident)
3c3dfce

was not the objective of this PR and maybe should be handled separately when merging.

@jbreue16

[jbreue16]

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[jbreue16]

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[schmoelder]

Please also provide links between modeling/interface like with the other models.

[jbreue16]

Ive added the general MCT equations to the documentation.
Since the model is rather unknown compared to our chromatography models, i think its fine having a description before we state the equations. The tracer transport should go into an individual subsection (where i think we should also cite a corresponding paper once its out).
@hannahlanzrath feel free to adjust my changes, I was not 100% sure about where every paragraph should go.

[hannahlanzrath]

So I had a look again at the Radial Flow Documentation that is currently up live on

https://cadet.github.io/master/interface/unit_operations/radial_flow_models.html

and spotted a few more Issues.

I will correct them in this PR but it should probably be squashed separately during the merge.

@jbreue16 @schmoelder

[jbreue16]

Theres actually another PR #193 in which we wanted to go through and fix the documentation, including radial flow.. glad you found and fixed those but no need to delve deeper into this here. I agree on making two separate master commits from this PR

[hannahlanzrath]

Ah sorry, I searched for a PR with the Radial Flow Doc and couldn't find one. Fixed the issues I mentioned an will just leave it at is now.

[hannahlanzrath]

Okay, with that last commit from my side this is ready to merge. Thanks a lot for contributing the equations!

[jbreue16]

Should we explicitly mention the results of the forum discussion in the MCT documentation, i.e. that the exchange rates are used to calculate the exchange flow wrt the volume of the outflow/source channel?
Maybe even a second use-case chapter on how to replicate the linear binding LRM with essentially the content of the forum post?

[hannahlanzrath]

I think that's a good idea to highlight and deepen the understanding of the differences between the models.

[jbreue16]

@schmoelder this PR is good to be merged from our side