Added exception handling for ImageIO class
Added AboutProject button
Added class diagrams for MVVM pattern
New class diagram shows new properties and names
Laid out foundations for model and viewmodel
Added NotImplemented exceptions
Added briefs for most comments and variables
Changed layout of UI controls
Added some messy layout for left panel

I don't know any better, but this is how the UI will look until all of the technical stuff is dealt with. Functional UI comes first, convenient and design comes second.
Added first implementation of Packer.cs
Hooked up Packer ICommands to Packer
UI Buttons bound

Nothing works yet though\!
Added further comments
Implemented Add button
Added edge case logic for atlas consisting one subsprite
Write pos in pixel coords to Subsprite instances during sort
Separated sorting from atlas drawing
Added XML doc creation with temp vals
No longer writes temp atlas to filesystem
XML doc now includes image path