Issue8 ficurve zap

OK this branch needs to be merged URGENTLY because it contains a MAYOR bugfix in load_models. There was a {}-{} to subtract rhs of an equation and the dx/dt term and then solve again for dx/dt. It allows one to write c*dv/dt on the left hand side of the equation. This does not work with out brachets!! It has to be "({})-({})". This caused the signs of the currents to be screwed up.