standalone ViewController with callback

Added the possibility to create the `RSScannerViewController` from code and set up the `RSCornersView` automatically. Also added optional controls (return, change camera, torch). Interface is both iPhone/iPod and iPad compatible. You can also set a preferred camera position when creating the ViewController.  - See sample Code
It is intended as a drop in code, so you don't have to create your own interface for scanning a barcode.