Merge pull request #478 from am11/master

Sprite: Added .png to validation
Image Paste: Adding pasted file to project
Img Opti: Fixed rounding issue with compression %
Sprites: File nesting, icons, minor tweaks
Sprites: Fixed blank output. Fixed #466
Sprite: Removed absolute file path in JSON file
Sprite: JPG & GIF support. Refactorings
Sprite: Removed border & refactored static code.