OK, reverted the matrix-vector classes and made them almost...

... compatible with the old API.
Matrix -> DMatrix, Vector -> DVector, project-wise
VectorspaceElement -> DVector
Matrix-vector back-compatibility
Grids, OK
VariablesGrid, operator DMatrix()
Symbolics fixed to the new API
Algorithmic base fixed to the new API
BDF does not work ATM.

Have to figure out how to use QR decomposition from Eigen here
ACADO integrators refactored.
Examples for ACADO integrators scope compile
Fixed Matrix class, ctor and P(S)D checking
Fixed qpOASES interface
Fixed OCP and Simulation classes
ACADO optimal control and simulation classes work, BUT:

- I had to disable BDF integrator code
- this means that BDF int. cannot be used at the moment