Update documentation

[schmoelder]

Many PR's have been merged recently, with many people contributing to the respective documentation.
We should review and overhaul the new parts of the documentation with at least two people of our group together.

Todo

• DG doc review
• github and website citing section (HL for example was confused on how to cite cadet. (JB: 1) emphasize one single paper 2) get rid of selected applications section, since this a) is about citing cadet and the models/methods implemented and b) will get out of hand quickly. Maybe move it somewhere else like a highlighted use-case section on the website 3) instead add a modelling section with e.g. crystallization, mct paper?)
• Fix surface diffusion salt state dependency documentation
• Fix boundary model documentation for FV (only 1 and 2 are allowed but 0,1,2,3 are documented)
• The following open reviews were moved to a new issue Review documentation #298 :
• radial flow doc review: end of modelling section of GRM, LRM, LRMP and interface at interface/unit_operations/radial_flow_models.html
• mct doc review at modelling/unit_operations/multi_channel_transport_model.html and interface/unit_operations/multi_channel_transport_model.html
• Michaelis Menten kinetics at modelling/reaction/michaelis_menten_kinetics.html#michaelis-menten-kinetics-model and interface/reaction/michaelis_menten_kinetics.html

[jbreue16]

Ive documented the radial flow as follows:

The modelling documentation for unit operation that supports radial flow now has a subsection with the corresponding equations.
Ive decided to use $\rho$ as the radial coordinate of the column since we are already using $r$ for the particle coordinates.
Thats also why I chose $P_c$ and $P$ for the inner and outer column radius, i.e. capital rho.

The radial flow interface is documented separately and only contains the changes that need to be made to get the radial flow variant of the corresponding model (changes are the same for all units).
The doc can be found under interface/unit_operations/radial_flow_models.html . I just thought its a little too hidden and we should probably add a reference to that page in the documentation of the unit operation interfaces.

A brief documentation for the parametert dependencies was added under interface/parameter_dependencies. Note that this feature is still work in progress and only a few dependencies are available as of now

[jbreue16]

I think we should use this PR to have a look at the documentation in general, including radial flow and DG.
We should also consider the developer guide (issue #166, PR #181)
and maybe fix #194, but the latter could also be addressed later when a general CADET landing page is created and CADET-Core gets a separate page and documentation

[jbreue16]

doxygen build is addressed in PR #89 and will also help guide developers.

Geometry sensitivities not supported by DG units: double check documentation and add the comment that these can also be computed with FD, or forward using cadet-fv units, as mentioned in #214

[jbreue16]

@AntoniaBerger the section "spatial reconstruction methods" might be an interesting read for you and you can also give us some feedback while we're at it.

[jbreue16]

@eric asked to add a description to how thats done since this is not an option supported by cadet itself

[jbreue16]

@lieres asked for changes since the theorem is about linearity and order of the method. the problem with oscillations is subordinate and should be described separately.

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[lieres]

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[lieres]

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