Bonus tasks

To get bonus points for the challenge you may want implement the following:

• Notify user when the internet connection goes down,
• Implement a custom overview screen state when there is no items to display and the internet is unreachable,
• Persist data between application launches so there is always some sensible data (i.e that isn't older than 1 hour) to display upon app's start,
• Incorporate more currencies to choose from on the details screen and think of a gracious way to present the picker UI (e.g. for 10 currencies a segmented control won't do anymore),
• Use a non-builtin transition animation between screens.