WICKET-4905 PagingNavigation: possible to call setStartIndex() earlier than onBeforeRender?

set the model and the start index in onConfigure(), not in onBeforeRender()

(cherry picked from commit 1724d89e5a16c4588f42cb551f028803dab193c7)
WICKET-5450 Double escaping when using EnumChoiceRenderer and DropDownChoice

(cherry picked from commit 3994cb3aa04e5b4d0fd5b8f015a1d53a5c8b1c4b)