adds enhancements to rotation


* replaces @current_rotation with two functions:
  device_orientation => current UIDevice orientation
  status_bar_orientation => UIApplication statusBarOrientation
* updates rotate(dir) to use device_orientation
* added rotate_home_button_to function
  rotate_home_button_to {down | up | left | right}

KNOWN ISSUES:

1. device_orientation is always "unknown" on the simulator until a
   rotation occurs
2. rotate_home_button_to can leave the device_orientation in an
   inconsistent state if a playback fails to rotate - happens if the
   view controller does not respond to rotations

https://github.com/calabash/calabash-ios/issues/156
https://github.com/calabash/calabash-ios/issues/72