New Feature - Gaussian Filter config values

[neshdev]

• Sigma value in the config object should be given in millimeters.
• Notes:
• This would make it slightly more complicated as we would need to know the x,y,z length of a voxel.
• Most MRI pictures have x and y of the same length, but the z length is normally smaller. (x == y, x > z, y > z). This is due the way the scans are taken.