Android: Added support for 'direction' to scrollTo.

Currently, Appium fails to scroll to text on views that scroll horizontally like HorizontalScrollView.

This fix will add a new option (direction) to 'mobile: scrollTo'. If 'horizontal' is provided (or if the view is a HorizontalScrollView), we will call setAsHorizontalList() before commencing the scroll.

I've also added a check for view's scrollability.