Moved the Quartz framework into the Frameworks folder in the Mac Plot Gallery project.
Removed some type casts that are no longer needed.
Override -[CALayer display] to skip creating a drawing context when not needed.
Collapse the axis set layer to save memory if it is not needed to draw the plot area border.
Fixed the iOS hosting view so it only removes notifications that it added itself. Removing all notifications sometimes caused problems with subclasses. Fixed issue #81.