[FEATURE] Image with non-(a, a, a) pixel spacing should be rendered with correct aspect ratio in GUI

[jesse-wei]

When loading an image with (a, b, c) pixel spacing, it is rendered with that aspect ratio in the GUI. However, it should be displayed with the aspect ratio of a (1, 1, 1) normal brain image. Additionally, this should work for all views.

Note that an image with (0.5, 0.5, 0.5) spacing actually looks correct in the GUI. So non-(1, 1, 1) doesn't necessarily have this problem. non-(a, a, a) has this problem.

This would involve modifying GUI/main.py resizeEvent.

We would need a boolean variable set in browse_files telling us whether the loaded image(s) have (a, a, a) pixel spacing or not.