Initial iterate is taken from a separate Python file now

The inline expression in the parameter file that we used previously is
too short and limited.  In particular, we want to be able to use the
same expression for error measurements.  However, for that we need
a function with a derivative.

src/harmonicmaps-stereographic-measurement.parset

@@ -56,7 +56,7 @@ baseTolerance = 1e-8
 energy = harmonic
 
 # Inverse stereographic projection
-initialIterate = "[2*x[0] / (x[0]*x[0]+x[1]*x[1]+1), 2*x[1] / (x[0]*x[0]+x[1]*x[1]+1), (x[0]*x[0]+x[1]*x[1]-1)/ (x[0]*x[0]+x[1]*x[1]+1)]"
+initialIterate = inverse-stereographic-projection
 
 ##########################################
 #   Discretization error measurements