Implementation of non-3D meshes

[Andres-MG]

The way 2D cases are handled is very confusing I think. These three attributes:

horses3d/Solver/src/libs/mesh/HexMesh.f90

Lines 72 to 74 in 41111c5

	logical :: meshIs2D = .FALSE. ! Is this a 2D mesh? default .FALSE.
	integer :: dir2D = 0 ! If it is in fact a 2D mesh, dir 2D stores the global direction IX, IY or IZ
	integer :: dir2D_ctrl = 0 ! dir2D as in the control file

are set during the pre-processing stage to a value that depends on the keywords in the control file and the mesh itself. It seems that this is done in this function:

horses3d/Solver/src/libs/mesh/HexMesh.f90

Line 1619 in 41111c5

subroutine HexMesh_CheckIfMeshIs2D(self)

but it seems to override the choice of the user in the control file.

I will not merge #158 until this is reviewed, as the characteristic length of the elements is now wrong in 2D cases, and methods depending on it (LES, shock capturing) will provide different results.

[loganoz]

I have pinned this issue so we don't forget.