hdf5: use microscope type to improve on light bandwidth guess when reading file

It helps to further distinguish between brightfield and fluo streams
gui visual range slider: avoid choking if range is null

min and max of range should not be the same, but if they are, don't crash.
tiff: ensure wave polynomial is saved with enough precision

saving the polynomial as int doesn't work as some of the values can be very small, better save a float.
tiff: save and restore tint metadata in TIFF file
gui: better distinguish brightfield data from fluo

use MD_USER_TINT as an additional hint