Added best_ff property to simplex.
Added best_ff property to simplex.

In case simplex encounters an error mid optimization run, best_ff
is used to return the best FF and not loose the progress that
has been made thus far.

ericchansen/q2mm,arosale4/q2mm,Q2MM/q2mm,ericchansen/q2mm,Q2MM/q2mm,arosale4/q2mm