Up and down arrows functional in layer manager

This PR makes the up and down arrows operational in the layer manager.

The markup is also changed so that `<i>` is used instead of `<a>` for the the first "up" arrow and the last "down" arrow, as suggested in https://github.com/geoadmin/mf-geoadmin3/pull/348#issuecomment-23412946.

Please review.

Currently the layer to the top in the map is at the bottom in the layer manager, and it looks like re2 has a different behavior. Should the behavior of re2 be retained? If so I change work on the required modifications, and create a new PR for that.