FireVoxel 262A is released

1.  Re-engineered the MGH (FreeSurfer)  Read support.  Added the MGH\MGZ   ABT Unit test.
2.  Paintbrush drawing at Rad=0:  cursor radius is now minimal but will always remain visible.
3. Defect fix:  When Brush painting, after a certain stroke the Left Mouse (LMB) button is released.  Then if user continued the painting, but press the LMB first and only then  Ctrl button (usually it is Ctrl then LMB), FireVoxel was connecting the previously finished stroke with the newly started one, thus making the unexpected brush segments.