Blender Git Loki

Voxel Size Edit: Fix text not readable when zooming in the viewport

Previously the scale of the text was using object space, so when working
with scaled objects or small meshes the size of the text was wrong. Now
it calculates a scale in screen space, so the text size should be much
more predictable

Reviewed By: sergey, Severin

Differential Revision: https://developer.blender.org/D7941