Refactoring TextureAtlas to abtract the packing process away to an external class
Renaming IDefaultExporter interface to IBundleExporter
Removing unneeded field from the TextureAtlas class
Made the frame origins rectangle for a frame added to the texture atlas be initialized with the dimensions of the frame
Adding a 'File a bug...' menu item under 'Help'
Refactoring SheetPreviewPicturebox's Unload() method to UnloadExportPreview()