Added ability to override default messages
#187: Adds the SirenAlertMessaging
struct, which allows for custom overriding of messaging in UIAlertController update modal.
siren.alertMessaging = SirenAlertMessaging(updateTitle: "New Fancy Title",
updateMessage: "New message goes here!",
updateButtonMessage: "Update Now, Plz!?",
nextTimeButtonMessage: "OK, next time it is!",
skipVersionButtonMessage: "Please don't push skip, please don't!")