optimize WebDriver module for issue #518, clear some typo by my previous commit, and add 'moveMouseOver' function

changes made by me:

* removed ```register_shutdown_function``` in ```_initialize``` to prevent uncertainties
* ``` $this->webDriver->manage()->deleteAllCookies();``` in ```_before```, if user wants to keep the same session between tests, he/she is the one to take care how tests work, this can be achieved by making helper class
* changed ```_after``` class, currently it only does something when user choose to ```restart``` session
* changed ```_afterSuite()``` to make sure webDriver object cleared after suite done
* added 'moveMouseOver' method
* corrected some typo from my previous commit