[FEATURE] Make it possible to manipulate the page order in the menu

At the moment the menu just takes the pages ordered by name and
you have no way to change the page order.

page_1
page_2
page_3

With this patch you can set the meta information "Order".
This will order the pages by number, any page that has no number will
fallback to the end.

page_3 (Order: 1)
page_2 (Order: 2)
page_1

You can disable it with the option "sortPagesByOrder" for the MenuViewhelper