router

A follow-up to chx' Menu needs to be torn apart.
(this linked thing is a wiki page, so no discussion possible over there)

What chx said:

1. Router system with access control.
1. Tabs with access control.
1. Menu links

These three have little to do in common and yet we keep them together.

Chx actually said more than this, but for now all I want is a problem description.

Changes that I hope we can agree on: