Added verticalOffset option to specify the top position of the message

+ Added verticalOffset property
+ Added variants of each public method to include verticalOffset
parameter
+ Set statusBar height as the fallback where no verticalOffset is
provided

This is especially useful when iOS7's topLayoutGuide.length property is passed, as it should automatically position the message at the bottom of the navigation bar or status bar (as applicable), in both orientations.

Annoyingly, the taller in-call status bar does not seem to adjust the length property of topLayoutGuide, so this would have to handled manually, AFAIK.

P.S. Sorry about the whitespace conflicts.