[BACK_INCOMPAT] Move "backgroundColor" from `fabric.Text` to `fabric.Object` (only works with text for now). Remove `fabric.Object#overlayFill`. Remove `fabric.Canvas.toGrayscale`, `fabric.Object#toGrayscale`, and `fabric.Object#overlayFill`. Version 1.3.5
Add x/y in `fabric.Rect#stateProperties`. Make `toObject` remove them when includeDefaultValues=false.
Fix includeDefaultValues to account for stateProperties of specific objects
Add rectangles optimization to Spray brush
Build distribution