Updated README and device orientation in iOS Cordova plugin

I noticed the following issue on a phone running iOS6:
In the iOS Cordova plugin, the camera overlay view was rotating into portrait mode (while the camera stayed in landscape).

Proposed fix (see code):
Add iOS6 method 'supportedInterfaceOrientations' to the scanner view.

Additional Notes:
I touched the README to address compiler errors (missing frameworks) that popped up when I built a new project using this plugin.