Updating the look for iOS 11

[TimOliver]

At WWDC 2017, Apple introduced a new, bolder look for iOS 11. As part of this, the lock screen was slightly redesigned, with the buttons having bolder fonts, and no longer hollowed out. This makes TOPasscodeViewController look somewhat dated on iOS 11.

At some point, I'll need to review the look of this library and see about updating it to match.

I don't actually like the filled circle button look of the iOS 11 lock screen, so I'm wondering if I can get away with just making the stroke width of those circle buttons thicker instead. Diverging from the official look also lessens the chance of this library getting rejected by App Review as well.