#97: Add Configurtion.WindowWidth and Configuration.WindowHeight

[davespoon]

Add WindowWidth and WindowHeight properties to Configuration. Add also ResizeWindow method to GoToUrl Add correspondent tests. ........ I decided not to change int? to uint? or ushort?, allowing user to deal with WebDriverArgumentException like it's done in Selenium Webdriver and other concise wrappers like python's selene. It could be changed later though ;)