Set min/max help text to value range

[banesullivan]

The min/max fields in the UI do not show the min/max range for each band and it can be tough to decipher what the value range is.

It would be great if we could do two things:

• Set the help text to include the actual min/max values for the selected band
• When initially hitting the up/down arrows, it is incremented from the actual min/max values