Cosmetic changes to make the code closer to prescribed Swift

Liked your code. I thought it could be slightly improved with a few edits here and there. My apologies for the myriad comments, I tend to commit my code in small chunks. Also fixed a couple of minor bugs: 1) The alert view's title for the 5 cases were all using the Success string constant, while there were 4 other title constants defined, 2) the switch's default case might have caused problems later on and wasn't needed since the switch block was exhaustive to begin with. Cheers!