MIP method of thicknessMethod probably don't consider the current slice orientation

### Description
When using MIP method (default thickness method with some >0 thickness slice setting) with non-axial slice, it displays some repeated pattern. It seems like the direction that max intensity is calculated is not perpendicular to the slice plane. I am not sure if this is the expected result of MIP, or it is really a bug.

For example, this is a part of coronal view without MIP method (slice thickness = 0)
And when MIP method is turned on, the pattern are repeated (and there is no such problem in the axial view).

#### Live Demo
Similar behavior can be found in the [geometries slice example](https://fnndsc.github.io/ami/#geometries_slice).
Set thickness to some value > 10. In some direction, you would see some ripple-like pattern and the bright area seems expanded.

### Browsers Affected
- [x] All
- [ ] Chrome
- [ ] Firefox
- [ ] Edge
- [ ] Safari 9
- [ ] Safari 8
- [ ] IE 11

### Versions
- AMI: locally using v0.22.0, don't know which version is used by the demo site (have cloned and run the latest code, it has the same problem.)
- THREEJS: locally using v0.93.0, demo site using v0.107.0