Support displaying float64/double NIFTI images

### Description
When trying to load a NIFTI with type FLOAT64, the error message `"Unknown data type: datatypeCode: 64"` is shown. This is surprising, as it seems as most of the code of the NIFTI parser (parsers.nifti.js) takes this data format into account (for the pixelType for example).

Additionally, I've seen that other viewers using the same [NIFTI-Reader-JS](https://github.com/rii-mango/NIFTI-Reader-JS) library are able to display this image format correctly (e.g. the [Papaya](https://github.com/rii-mango/Papaya) viewer).

#### Live Demo
https://fnndsc.github.io/ami/#viewers_upload

#### Steps to Reproduce
1. Go to the viewer example above
2. Upload this sample file : http://fast.hevs.ch/temp/double.nii (or any other FLOAT64 NIFTI image)

#### Expected Results
The image should be loaded correctly, as is the case with UINT8, INT8, INT16, UINT16 and FLOAT32 types.

#### Actual Results
Only an error message is shown and the file is not loaded correctly.

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

### Versions
- AMI: v0.32.0
- THREEJS: r106