Replace eigen-quadprog
The current QP solver seems to have some problems.
First of all, the unit tests sometimes fail in a seemingly random way, suggesting issues in memory management.
Second of all, the simulation sometimes freezes altogether while using the QP solver. This must be a bug inside the solver itself.
I think I will copy some code from eigen-quadprog. But we should make a separate repo with that code, some day soon.
Otherwise, any other suggestions? qpOASES, for instance?