HDF5 Read & Write

[lauramurgatroyd]

• Allows reading of HDF5 files to vtkImageData with HDF5Reader, and reading a cropped version of the image with RequestSubset
• Allows writing of vtkImageData to HDF5 files with write_image_data_to_hdf5
• Resampling of HDF5 with cilHDF5ImageResampleReader
• Tests of the above

To do:

• Test RequestSubset works when selecting a channel
• Possibly rename methods
• Add resample reader

[lauramurgatroyd]

The only change to conversion.py that isn't just formatting is the addition of this cilHDF5ImageResampleReader class

[lauramurgatroyd]

Note:
I had to place the hdf5 methods into a new file hdf5_io. This was necessary to avoid circular imports.
The problem was that the cilHDF5ImageResampleReader reader lives with the other resample readers in conversion.py, and this class requires the use of HDF5Reader. Also the ImageDataCreator in io requires the ResampleReaders. So the hdf5 classes couldn't be placed in io.

[lauramurgatroyd]

See #127 for improvements to structure of the resample reader

[lauramurgatroyd]

Once #150 is working and merged, can check that the HDF5 test runs with the gh-action, and then will merge this

[lauramurgatroyd]

The unit tests pass locally but currently fail when run in the github action. Maybe there's a problem with writing the files?

[lauramurgatroyd]

It is now fixed!

[lauramurgatroyd]

Waiting on fix of #150, otherwise we agreed this was ready