DNS views, part 22

Issue #26

Begin phase 2 : RR virtualization

This commit provides:
- document new database schema:
    doc/netmagis.org/tables.fig
- push back view id from peripheral tables
    (dns.rr_*) to main RR table (dns.rr)
- emulate old behaviour (multiple views in
    the trr array returned by read-rr-by-*)
    in access functions (rr-*-by-view)
- context is now always single view (before,
    it was single view except in www/cgi/add
    and www/cgi/admlmx)
- read-rr-by-name now needs a view id
- check-authorized-host now needs only one view
- no more role web
- menu-view procedure no longer issue a listbox,
    but always a menu (or hidden field)
- put a show-stopper on eq-graph-status to
    remember to adapt it for views