Deprecated scanningIsAvailable method

`scanningIsAvailable` wasn't very descriptive. If the device has a camera, this method would return YES even if the user rejected permission to use the camera. See [#10](https://github.com/mikebuss/MTBBarcodeScanner/pull/10)
Added launch screen, iPhone 6+ resolution support
MTBBarcodeScanner Release 0.1.8
Merge branch 'release/0.1.8' into develop