Update example for iOS 8 beta 5 and Xcode 6 beta 5

Removes the note and code for choosing special colors for the UILabels. In
beta 5 (and probably earlier betas after 1 or 2) the color of the UILabel no
longer affects its appearance when added to a vibrancy UIVisualEffectView. Much
more intuitive.

Make the scroll view bouncy. I think this feels better.

Keep up-to-date with Apple's Swift changes for UIView's declaration. E.g.
superview is now a regular optional field (`UIView?`).

Xcode 6 changed the imageset format; committing new Contents.json files.