Fix crash when back to other app while this app is killed.
Remove SlideListActivity and change UI flow. Remove thumbnail files. Do not use json index file anymore.
Treat no image chosen as cancel. (should I handle this on MultiGallery?)
Fix slides. Previous check-in break slide import.
Change icon from slides to start because UI flow changed.
Ver 2.2.
Implement cancel for MultiGallery.
Make inval region smaller.
Ver 2.3
Make undo compression asynchronous.
Ver 2.4