Store a PixelPaint project in a .pp file (as there doesn't seem to
be any real standard on this). It's a very simple json file that
contains the bitmap as a base64 encoded bmp.
The most used feature of any image editor, undo. Each tool now
notifies the ImageEditor that they completed an action, where
it'll take a snapshot if its current state.
For now, a snapshot is just a copy of the whole image and its
layers. There's a hard limit on the amount of actions it stores.
We use this to automatically update the thumbnail in LayerListWidget
when you draw into a layer. We also use it to repaint the ImageEditor
when the image changes somehow. :^)
Instead of using a TableView to show the layer stack, let's build a new
custom widget for this purpose and give it some neat features!
This patch also introduces an ImageClient interface for Image to notify
interested parties about things happening. The LayerListWidget is the
first ImageClient and listens for "layer added" and "layer removed"
notifications. :^)
ImageEditor now supports panning (Ctrl+MiddleMouse) and scaling (Wheel)
the image. This took a lot of unpleasant coordinate math, but now it
actually kinda works and feels awesome! :^)
