fix on plotting 3D power spectrum

Fix on the three Axis label display,
label set to display Greek and Mathmatic symbols.

add two parameters:

setMax: (float Type) set Z Axis Maximum to assigned value. Use Maximum
of input data 'Z' if not set.
setMin: (float Type) set Z Axis Minimum to assigned value. Use Minimum
of input data 'Z' if not set.