NXP-13987: add convenient methods and class to test vocabularies

Conflicts:

	nuxeo-functional-tests/src/main/java/org/nuxeo/functionaltests/Locator.java
	nuxeo-functional-tests/src/main/java/org/nuxeo/functionaltests/forms/Select2WidgetElement.java
NXP-13987: add test on vocabulary and select2 behavior on entry deleted
NXP-13987: disable selenium test on vocabulary
NXP-13987: ignore StaleElementReferenceException in wait for loading
NXP-13987: remove selenium vocabularies test
NXP-13987: tear down in the test
NXP-13987: remove useless select
NXP-14430: adapt functional tests backport for 5.8