Blender Git Loki

Image Editor: implement FKey to call 'View All' with 'fit_view'
This mimics the behaviour we have in the Clip Editor.

I personally would prefer if we had no border once in fullscreen
(current border is 5 pixels).

I will consult Sergey Sharybin first to see if we can change that in the clip editor as well (though there I
believe the border is useful - the bottom of the editor is used to indicate 'tracked' frames.