DLS I16 loader

[DanPorter]

Implementation of CDIUtils for the I16 beamline at Diamond Light Source.

• I16 uses single NeXus files per scan so this has lead to a change in inputs for certain of the loader functions. The NeXus files contain all the detector details and this is extracted.
• I16 has a 6-circle diffractometer involving 4 Eulerian rotations of the sample, however I can't figure out how to add more than 2 - some advice would be appreciated on how to do this (see the TODOs).
• A geometry entry has been added for I16. This has been tested on the beamline and should be correct.
• I've added an i16 specific notebook and made some changes to the prepare_bcdi_notebooks.py script to allow this to be run (it will run automatically if the instrument environment variable is present).

The notebooks run on the beamline in a prepared python environment including PyNX.
Still todo: I need to make some changes to allow cluster submission at DLS.

[DanPorter]

Changes made above. Thanks for the suggestions about multiple axes - these will have to wait for a future PR, along with cluster submission changes. I suggest this is merged as is as it works for standard rocking scans in the vertical geometry.