Dynare++: ensure that all calls to BLAS/LAPACK use the correct LD values

Many BLAS/LAPACK calls were making the assumption that LD==rows when passing
matrices. In some cases this was correct (because of implementation details,
in particular because how the copy constructor of GeneralMatrix is implemented).
But in other cases it was a bug.

With this commit, the actual value for LD is systematically used (this fixes
existing bugs and prevent possible future ones if the implementation details
were changed).