The function leica_OME_tiff is doesn't work if images are not taken in 4+1 channels

[mgcizzu]

The function leica_OME_tiff has a line which hard-codes the shape of the OME tiffs to 5 channels (4+DAPI), see below.

stacked = np.empty((5, 2048, 2048))

This makes it impossible to work with images acquired with more or fewer channels than the "Nilsson standard" way. I realised this while trying to work with 5+1 images.

We should come up with a flexible way to specify this (ie, a variable defaulted to 5 unless otherwise specified?)