Window Handles - getWindowHandle and getWindowHandles
1. getWindowHandle return session id of current window (String)
2. getWindowHandles return session id of all windows opened by webdriver (Set<'String'>)
3. To switch between windows use command - driver.switchTo().window("give session id")
4. driver.close() - Close current window opened by webdriver, Still webdriver session is alive
5. driver.quit() - Closes all windows opened by webdriver i.e, it kills the webdriver session
