Connected photo editing in a proper way
Image buffer as a gproperty in a photo slide
Image buffer as gobject with gproperties
Changed class name from photo to image buffer
Slide or slideshow widget can be passed to editing specific handlers
refs #662
Initialize image buffer in the photo editing view
Changed name of photo editing to valid english name
refs #662
Image buffer for editing view defined in json
Fixed imports conflict
refs #662
Image buffer not in json
Adjusted photo editing handlers
refs #662
Not doubled viewer handlers definitions
refs #662
Merge branch 'master' into editing-connect

Conflicts:
	pisak/viewer/app.py
	pisak/viewer/handlers.py
	pisak/viewer/photo_edition.json
	pisak/viewer/widgets.py
Merge branch 'editing-connect' of ssh://git.nimitz.pl/pisak into editing-connect
change size of butts in photo_editing stage, kick out progres bar, temporarly attach start_button to photo_stage
refs #580