Use objc syntax for setting properties

Setting the segmentCount and selectedSegment properties doesn't appear
to work on 10.9. Ironically these properties had their old-style
getter/setters removed in 10.10, but the old syntax still works there.
Unsure if this is a CocoaScript quirk, but old-style syntax seems to be
the most compatible option.
Keep Sketch in the foreground when previewing
Update CHANGELOG for release