Make getDirectionFromString a static method
Make getDirectionFromString a static method

Co-authored-by: Joshua A. Anderson <4840522ac04c6557f2a84eb817629fe81427a26a@umich.edu>
joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue,joaander/hoomd-blue