Support for biomedical image formats NIFTI

[ktsitsi]

This draft PR:

• Adds support for NIFTI images in TileDB-Bioimaging
• Roundtrip has been tested and is working using the from_bioimg, to_bioimg API calls and the respective Converter.Nifti
• The original & exported images are renderable by Slicer
• Unit-tests (in-progress)
• Other sample images apart from visiblehuman
• Differences between Nifti1Images and Nifti2Images (Will split it into a different ticket)

from tiledb.bioimg import from_bioimg, to_bioimg 
from tiledb.bioimg import Converters
from_bioimg('./tests/data/nifti/visiblehuman.nii', './tests/data/nifti/tiledb_out/nifti_sample.tdb', converter=Converters.NIFTI)
Ingesting level 0: 100%|██████████| 256/256 [00:05<00:00, 46.45tiles/s]
Out[4]: tiledb.bioimg.converters.nifti.NiftiConverter
to_bioimg('./tests/data/nifti/tiledb_out/nifti_sample.tdb', './tests/data/nifti/nifti_roundtrip.nii', converter=Converters.NIFTI)
Out[5]: tiledb.bioimg.converters.nifti.NiftiConverter

Source of the sample test images are from nibabel https://github.com/nipy/nibabel/tree/master/nibabel/tests/data

[XanthosXanthopoulos]

Some properties get their value set as NaN which is not a valid JSON type and should be set to null

[XanthosXanthopoulos]

NIT

Suggested change

	# but in special cases can be degnerate into channels
	# but in special cases can be degenerate into channels

[XanthosXanthopoulos]

How would you detect such case? May be useful to log some warning message.