Adjust iPhone and iPad storyboards

Wasn't happy with the layout of both the iPhone and iPad UI. As
I've decided not to include any passphrase management in the
initial release of the app, it makes sense to situate the 'New
Passphrase' button at the bottom of its container, and the
'Replace' & 'Copy' buttons at the top of their container. By doing
this the overall layout is cleaner.
Remove NSArray category

Wasn't being used. Will be folded into fiorello.
Add timer that removes passphrase from pasteboard after 30 seconds
Update README