New Feature - Gaussian Filter config values

- 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.