Add native execute script action TwoPointerGesture

To support multi touch gesture such as pinch-in, pinch-out with two fingers.

The implementation is original from Android uiautomator. http://grepcode.com/file_/repository.grepcode.com/java/ext/com.google.android/android/4.4_r1/com/android/uiautomator/core/UiObject.java/?v=source

```python
driver.execute_script("TwoPointerGesture", { 
	"startPoint1X":20, "startPoint1Y":900,
	"startPoint2X":20,"startPoint2Y":900,
	"endPoint1X":20, "endPoint1Y":900,
	"endPoint2X":400, "endPoint2Y":900, "steps":40})
```