(WIP) Refactor Sheeter for better open/save support
Over load/save mechanisms

 - ad methods "load", "save" and "saveAs" which can be overridden when
   using a platform that provide a more powerful filesystem api
 - display unsaved changes
 - minor styling
Allow loading/saving images using the native windows apis
Update alchemy.js
Styling
Styling overhaul
Update spinner background
Show message toasts after saving sprite sheets
Clean windows 8 specific code
Use css "transform: translate(...)" insead of top/left because it is faster