Selection not saved with session

[1j01]

The selection isn't saved along with the session, so if you have a selection and you refresh or close/reopen the app, a chunk of your image will be missing (irreversibly).

This is compounded by the fact that you don't even need to move the selection for it to cut the selection out of the image. This is not how it works in mspaint, and not how it should work. See #28

It would also be good to save some other data with the session, like the selected tool, tool options, the viewport, the palette, etc.