feature(ngScenario/dsl): trigger event with keys and mouse position

+ element(selector, label).trigger(eventName, keys, x, y) trigger eventName event on an element with keys and mouse position
+ element(selector, label).mousemove(keys, x, y) mousemove an element with keys and mouse position
* element(selector, label).mousedown(keys, x, y) mousedown an element with keys and mouse position
* element(selector, label).mouseup(keys, x, y) mouseup an element with keys and mouse position
fix(ngScenario/dsl/test): use clientX/clientY instead of pageX/pageY to test mouse position for IE8
+ ie8 supports for mouse event