Allow swiping fullscreen images to exit view.

[olorin99]

Swiping fullscreen image up or down greater than 1/3 of the view height exits the view. Otherwise the image will animate back to center of view.

[jwr1]

This doesn't seem to work with zooming in/out (of the image) anymore? Is there a way to support both?

[olorin99]

Ok flutters builtin InteractiveViewer kinda sucks. It internally uses a GestureDetectors onScaleStart, onScaleUpdate, onScaleEnd to handle all interaction types, which doesn't seem to work great for panning. I keep getting instances where I pan the image and the onInteractionEnd callback never triggers leaving the image floating weirdly off center of screen. I'll look for a third party library which handles panning better and redo this PR.

[olorin99]

This should work now. Used https://pub.dev/packages/extended_image which also has some other nice to haves like simple editing which might use down the road.

[jwr1]

Looks good, thanks!