Added preliminary support for Gtk3

Not all plugins work, but example programs do.
More fixes for Gtk 3

For reference viewer:
- All global plugins except Thumbs and WBrowser are working
- Some local plugins are working

This commit also includes a bug fix for auto cut levels where the saved
preference was not being used initially.
Fix for a renamed module in the ipython source
Misc updates to Ginga

- split Zoom plugin into common base class + widget specific subclasses
- new Timer module replaces klunky use of widget timers in some cases
- updates to Zoom and Thumbs to use new Timer module
- fixes to ipg module to work with older and newer versions of IPython
Efficiency improvements

Efforts to improve speed of entire rendering pipeline and widget
specific redrawing

* Decent improvements, Ginga can now render HD video (no sound) at 30
  FPS on older hardware (see scripts/example1_video.py).  This
  translates to a slightly speedier feel overall for many operations
  viewing regular scientific files.
* Fixed a bug that gave an error message of
  Callback.py:83 (make_callback) | Error making callback 'field-info':
  'Readout' object has no attribute 'fitsimage'

* Version bump
Fixed a logging bug for ipg (ipython notebook) module
Changed default toolkit to Qt

This is for python3 issues--cairo still needs some new development on
Gtk3/python3.
Bug fixes for Mac version of ipq

- added show() and load() methods to Ginga ipython notebook viewer
- GUIs now raise above the page when activated
- should have fixed a segfault on Mac OS X
Fixes for error messages in setup.py
Updated toolkit configuration options and color management

- added toolkit module to let user specify exact toolkit to use
- updated color management code
  - common profile conversions are faster if profiles are found
Added logger to RGBMapper
Fixed bug for systems without PIL installed
Merge branch 'master' of github.com:ejeschke/ginga