getRatio assumes a particular reaction direction

[dczielinski]

The function getRatio returns the equilibrium constant of reactions that a particular metabolite is involved with. This is intended to be used to get the dissociation constant of activator or inhibitor reactions, but it just grabs the equilibrium constant of the reaction without regard to the direction of the reaction. Safer behavior would be to check the direction of the reaction so that a dissociation constants is always returned (as opposed to an association constant if the reaction is defined in the opposite direction as expected). Given the way that activator and inhibitor reactions are defined currently, this is not a practical issue, but could become an issue if we change the usage case of this function or how we define activation/inhibition reactions