First crack at ds9 style color map shift/scale in X/Y

	modified:   ginga/FitsImage.py
	modified:   ginga/Mixins.py
	modified:   ginga/RGBMap.py
	modified:   ginga/gtkw/ColorBar.py
	modified:   ginga/imap.py
	modified:   ginga/qtw/ColorBar.py

- Ginga now uses a ds9 style color map change when using the interactive
    adjustment function
  - moving the cursor in Y adjusts the scale of the color map
  - moving the cursor in X adjusts the shift of the color map