Concerning #566: Renamed bfgs->limited-memory
Concerning #566: Moved Hessian options to derived classes, IPOPT naming convension for CasADi classes.
Converning #716: Removed workaround for gradients with no nonzeros. Should not be needed when gradient() is queried instead of jacobian()
Concerning #566: Updated SCPgen examples
Concerning #566: Fixed unittests