customize footer entries

[LarsRabe]

related to #132

I would love to see the possibility to change the positions of the footer entries. The up-/down-order in the webtrees footer menu could then represent | position 1 | position 2 | position 3 | | position 4 | position 5 | position 6 |

[JustCarmen]

The layout is now:

| position 1 | position 3 | position 5 | | position 2 | position 4 | position 6 |

Note that the contact-links footer takes two positions.