Need consistent Matlab IO in Seg3D

Matlab IO needs to be consistent within Seg3D.

Built with master Seg3D v2.4.4 on OSX 10.14.6 with Qt 5.15. 

To test:
Exported a .nrrd data layer as a MATLAB file and read back into Seg3D. 
Changed from node to cell. 
Origin shifted from [229.26,-126.419,405.421] to [229.76,-125.97,405.87].

This issue closes #65 .