[Timob-17744] iOS8: Feature to check if device can support touch ID

Additional feature that can be used to check if the device supports touch ID authentication. 
Sample code:
```javascript
	var result = TiTouchId.deviceCanAuthenticate();
	if (!result.canAuthenticate) {
		alert('Message: ' + result.error + '\nCode: ' + result.code);  
	} else {
		alert('device can authenticate');
	}
```