[3.2][ticket/12662] Reorganize and modernize the header navbar

https://tracker.phpbb.com/browse/PHPBB3-12662
http://area51.phpbb.com/phpBB/viewtopic.php?f=108&t=45679&start=60

![updated](https://cloud.githubusercontent.com/assets/3015760/3210923/13dcb72a-eef0-11e3-85a3-b553fad8fbda.png)

Logged out
![loggedout](https://cloud.githubusercontent.com/assets/3015760/3208288/085885d2-ee28-11e3-89f8-f733f0dbb24e.png)

PHPBB3-12662
This linklist has been almost completely gutted. Keeping it as a `linklist` will cause the `forum_fn.js` to process it (which is useless now).

But removing the link list and simply have this as a `<span>` with float:right will make the `<!-- EVENT index_body_linklist_before -->` and `<!-- EVENT index_body_linklist_after -->` kinda awkward.

Any suggestions?