After removing the 3rd component from the Darcy velocity
and testing for a tight fit.

Alse remove unused computation from computeSecondaryVariableConcreteWithVector().

for consistency.

and removed the tests for the staggered scheme from LiquidFlow temporarily.

 in creating of the instances of classes of coupled processes.

 and added a OGS_FATAL checking for the global vector of the solution of
 the previous time step

that is originally for the monolithic scheme.

[HT] Modified the velocity calculation in order that it can be used for both the monolithic and staggered schemes.

[HT] Moved the computation of the coefficients of the heat transport equation to two new member functions.

[HT] Changed the name and the type of the material property member of HT, and

took the forward declaration of the type of that member.

 from the two classes of coupled term.

[Coupling] Changed the members of the coupled term,

 which only contains the solutions of the coupled equations.

[Coupling] Modified the process definitions in Process/HT for the assembly for both of the monolithic scheme and the staggered scheme.

 in one class either with the monolithic scheme or with the staggered scheme.