Add backgroundAlpha property to 2D and 3D text overlays
Render with backgroundAlpha property
Fix voxel size text display
Remove dead code that's causing problems
Update scripts with text overlays to use new backgroundAlpha property
Merge branch 'master' into 20202
Merge pull request #3917 from ctrlaltdavid/20202

CR for Job #20202 - Add "backgroundVisible" property to text overlays