Improve webdriver functional test library

This is a global issue for minor improvements around nuxeo webdriver library

• Use the page factory pattern with @required on @FindBy Webelements as much as possible (rather than findElementUntil).
• Adding vocabularies in the admin center.
• findElementWithTimeOut only works in the whole page, users should be able to find an element inside another element
• save the last screen shots in target folder if possible. in the system temp dir otherwise .