"Fix" a weird retina rendering error in the root border view

note: the fix is to draw a single-point rect over a missing pixel. no idea what's wrong but it comes from a bug in CGContextReplacePathWithStrokedPath
Merge remote-tracking branch 'origin/master'
Make the single-pixel fix to the root border view apply to all display scales - since it doesn't affect non-retina and I didn't like querying UIScreen.mainScreen
Add an app icon