First cut at handling different coordinate systems

	modified:   ginga/AstroImage.py
	modified:   ginga/BaseImage.py
	modified:   ginga/Control.py
	modified:   ginga/gtkw/GtkHelp.py
	modified:   ginga/gtkw/plugins/Info.py
	modified:   ginga/gtkw/plugins/Preferences.py
	modified:   ginga/qtw/QtHelp.py
	modified:   ginga/qtw/plugins/Info.py
	modified:   ginga/qtw/plugins/Preferences.py
	modified:   ginga/wcs.py

- Heretofore Ginga just displayed world coordinate info based on FK5
- If AstroPy is installed, Ginga will use it to support different WCS
   coordinate reporting systems: icrs, fk5, fk4 and galactic.
- Preference is currently handled on a per-channel basis (this may change)
Enhancements to Cuts plugin, partial commit

	modified:   ginga/FitsImageCanvas.py
	modified:   ginga/gtkw/plugins/Cuts.py
Bug fix for bad coord transformations

	modified:   ginga/wcs.py

- ginga now correctly follows the transform_to() protocol defined for
    coordinates if astropy is installed
- it makes a reasonable guess as to the initial coordinate system based
    on the FITS header
Factored out common code of plugins to a base class

	modified:   ginga/gtkw/plugins/Cuts.py
	new file:   ginga/misc/plugins/CutsBase.py
	modified:   ginga/qtw/plugins/Cuts.py
Merge branch 'advcuts'
Enhancements to Ginga FITS viewer

- Reorganized cairo drawing into its own module
  - will like refactor FitsImageGtk class to subclass FitsImageCairo
  - FitsImageCairo class allows rendering onto any cairo surface (PDFSurface,
     PSSurface, etc)
  - sample program in scripts/fits2pdf.py

- Added a colors module to make colors precise across toolkits
  - initially based on X11 rgb.txt defined colors

- Small enhancements to the Cuts plugin
  - typing 'v' while hovering the cursor will give you a vertical cut through
      the image
  - similarly, typing 'h' will generate a horizontal cut
  - removed "drawing" types of vertical/horizontal cuts until it has been
      thought through a little more
Refactored FitsImageGtk to subclass FitsImageCairo

	modified:   ginga/AstroImage.py
	modified:   ginga/cairow/FitsImageCairo.py
	modified:   ginga/gtkw/FitsImageGtk.py
	modified:   ginga/wcs.py

- also includes a fix for a bug where Ginga was failing to load images
     with no WCS info
Refactored FitsImageCanvas classes

	modified:   ginga/BaseImage.py
	modified:   ginga/FitsImageCanvas.py
	modified:   ginga/cairow/FitsImageCanvasTypesCairo.py
	modified:   ginga/qtw/FitsImageCanvasTypesQt.py

- base class now handles properly non-gui aspects of the forms
- graphics items are defined by the base class item + platform specific
    mixin class

- fixes an issue in Cuts plugin where the cut was not moved from the
    middle of the line
Fix for Thumbs (Qt) plugin auto scroll

	modified:   ginga/qtw/plugins/Thumbs.py
First attempt at zscale auto cuts

	modified:   ginga/AstroImage.py
	modified:   ginga/AutoCuts.py
	modified:   ginga/BaseImage.py
	modified:   ginga/wcs.py
Modification by eteq to change plotting style for Cuts

	modified:   ginga/gtkw/Plot.py
	modified:   ginga/qtw/Plot.py
Add .gitignore
Add .travis.yml