[FIX] Report: use ir.config 'report.url' key as base url if it exists

Browse ir.config 'report.url' with superuser as
the user may want to restrict access of this key to the public
[ADD] web: add a route '/web/dbredirect' to ensure the connection to the right database via the get param db.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64