Register file types - jpeg, jpg, png, gif

Now we can open images via Finder, and drag & drop on dock icon.
Read allowed file types from Info.plist
Cosmetic
Cosmetic
Add About panel
Cosmetic
Move duplicate: from AppDelegate to WindowController

When About panel was a key window, `Duplicate` action raised exceptions.
Add Move to, which move file with save panel

Also undo action is available.
Add Copy to, which copy file with save panel