Add calibrateAxis signature with units

FormatTools#calibrateAxis now has a signature that can also accept a
unit string, to update the units of the axis in one call.
Write actual ICS units

Instead of always writing "microns" let's write whatever unit is
actually attached to the axes.
Set ICS units

The units string was being parsed but never actually used when
populating Metadata axes.

Now, we set the units if a "parameter units" entry is present.