Add Multicomponent Freundlich LDF isotherm.

[ronald-jaepel]

This PR continues work by @sleweke to add the multicomponent Freundlich isotherm to CADET-Core.

I've rebased the branch onto master.

Status and ToDos:

• Add Flux and Jacobian Implementation
• Add tests
• Complete tests
• Add documentation

The Freundlich isotherm works in all tests configurations I threw at it (both components c_p > 1, cp == 0 and cp < 0).

[ronald-jaepel]

For reference, here's the current state of the documentation.

A multi-component extension to the classical Freundlich adsorption model.
A linear driving force approach is applied to obtain a kinetic form.

$$$ \begin{aligned} \frac{\mathrm{d} q_i}{\mathrm{d} t} &= k_{\text{ldf},i} \left(q_i^* - q_i \right) & i = 0, \dots, N_{\text{comp}} - 1 \\ q_i^* &= k_{f,i} c_{p,i} \left( \sum_j a_{ij} c_{p,j} + \tau \right)^{1 / n_i - 1}. \end{aligned} $$$

Here, $\tau &gt; 0$ is a small constant that ensures numerical stability.
In a rapid-equilibrium setting with a diagonal matrix (i.e., $a_{ii} = 1$ and $a_{ij} = 0$ for $j \neq i$), the traditional Freundlich isotherm is recovered.

For more information on model parameters required to define in CADET file format, see :ref:multi_component_ldf_freundlich_config.

Multi Component Linear Driving Force Freundlich
===============================================

**Group /input/model/unit_XXX/adsorption – ADSORPTION_MODEL = MULTI_COMPONENT_LDF_FREUNDLICH**


``IS_KINETIC``
   Selects kinetic or quasi-stationary adsorption mode: 1 = kinetic, 0 =
   quasi-stationary. If a single value is given, the mode is set for all
   bound states. Otherwise, the adsorption mode is set for each bound
   state separately.

===================  =========================  =========================================
**Type:** int        **Range:** {0,1}  		    **Length:** 1/NTOTALBND
===================  =========================  =========================================

``MCLDFFRL_KLDF``
   Rate constants in linear driving force approach

**Unit:** :math:`s^{-1}`

===================  =========================  =========================================
**Type:** double     **Range:** :math:`\ge 0`   **Length:** NCOMP
===================  =========================  =========================================

``MCLDFFRL_KF``
   Proportionality constants

**Unit:** :math:`m_{MP}^{3}~m_{SP}^{-3}`

===================  =========================  ==================================
**Type:** double     **Range:** :math:`\ge 0`   **Length:** NCOMP
===================  =========================  ================================== 

``MCLDFFRL_EXP``
   Freundlich exponent

===================  =========================  ==================================
**Type:** double     **Range:** :math:`\gt 0`   **Length:** NCOMP
===================  =========================  ================================== 

``MCLDFFRL_A``
   Component influences in row-major ordering

**Unit:** :math:`m_{MP}^{3}~mol^{-1}`

===================  =========================  ==================================
**Type:** double     **Range:** :math:`\ge 0`   **Length:** :math:`\text{NCOMP}^2`
===================  =========================  ================================== 

``MCLDFFRL_TAU``
   Small constant that ensures numerical stability

===================  =========================  =========================================
**Type:** double     **Range:** :math:`\gt 0`   **Length:** 1
===================  =========================  =========================================

[ronald-jaepel]

I got some comments from collaborators, so this PR will need work before it can be merged. I can take care of it after my return but I'll also forward you the email. Can't do much more from my phone atm.

[ronald-jaepel]

The typos have been fixed and this is imo ready for review.

[jbreue16]

Reviewing this, it just came to my attention that many binding tests are actually not part of the CI, right? e.g. the one defined here in this PR..
But this is an issue on its own (just opened #356 ), the changes you made look good to me, tests run, I think this can be squashed and merged.