Add iOS Wallet Button.

This pull request adds the iOS Wallet button with a disclaimer-type-of-thing modal when clicked.
How it looks: http://puu.sh/8kBIA.png
Modal: http://puu.sh/8kBJk.png

The "I Understand, Let's Go!" button goes to the MyDoge Appstore Page.
https://itunes.apple.com/app/mydoge/id805178886