Notable changes are:
* Filename for saving/loading device settings can be specified.
* improved calculation of auto enhancement values
* Enhancement options (gamma, contrast, brightness, rgb default
and negative) are saved as device settings.
* Auto enhancement and pipette functions calculate enhancement
values for each color now.
* Options rgb default and negative are added to preferences.
* pipette functions: middle mouse button defines shadow/gray/highlight
for color components, left mouse button only defines gray values!
