Add missing docs about External Function SMA model

Adds the missing file format specs for the External Function Steric Mass
Action binding model. Also adds the formulas to the "Binding Models"
section of the manual.
Add missing Matlab wrapper of External Function SMA

Adds the missing Matlab wrapper class of the External Function Steric
Mass Action binding model.
Fix log-transform of bounds in fitColumn script

A wrong index (j instead of i) caused the log-transformed bound
constraints to be complex values in the fitColumn Matlab script. This
typo is now fixed.