Remove unnecessary double clear when rasterizing a gradient
Initial buffer merge implementation
Use createBrushEvent in Picture unit tests
Always have undo states in Picture buffers
Refactor adding buffers to use the event mechanism
Add blamePixel tests
Do not display buffers whose creation is undone
Fix misplaced index initialization in undoEventSessionId
Fix undoing merge events from a Picture
Implement BrushEvent picking and translating
Fix animation sometimes repeating events
Keep the last buffer by default when undoing
Don't draw or playback undone buffers
Skip non-rasterized events when animating
Rename removedBuffers to mergedBuffers, removed buffers won't be there
Implement marking buffers in the stack as removed
Add ability to query PictureEvents whether they change the buffer stack
Allow removing a buffer multiple times through redoEventIndex
Handle insertion of merge events correctly
Implement moving buffers in the stack and in-sequence undo for it