andorshrk: update comment based on the feedback from andor
driver andorcam3: diagnose a bit the error when the camera cannot be found.

It happens so easily, for so many reasons that it should help us a bit to quickly fix problems with the configuration.
use importlib instead of __import__

slightly cleaner
hdf5: support exporting MD_WL_LIST

was able to read it (back), but could only export MD_WL_POLYNOMIAL. Now support both.
tiff: fix error loading 3D array

Still only support when the 3D array is one block, but a typo was preventing to even work in such a case.
acq calibration: add test case for spectrum calibration

everything passes now...
acq calibration: test for AR calibration data

passed