Support application tint color for iOS 7 applications

Usage:

```ruby
class AppDelegate < ProMotion::Delegate
  tint_color "#D3541F".to_color # Using Bubblewrap's color convenience method
  # or
  # tint_color UIColor.greenColor

  def on_load(app, options)
    # whatever
  end
end
```

It's working, but I can't seem to get the test right. Any ideas @jamonholmgren  or @silasj?