[FIX] mass_mailing: possibility to subscribe again to a mailing list

It was not possible to subscribe again to a mailing list once unsubscribed
[FIX] website_sale: confirm sale order on payment_confirmation

Same behavior than in saas-5
[FIX] web: multiple opened modal need fixing since bootstrap lib update
[FIX] website: slug: fallback to positive ID when slug appears to contain a missing negative ID

In some rare cases database records have negative IDs,
so the slug URL could look like /foo--20. This could
be mistaken for a slug ending with a `-` and a positive ID.
The latter is not supposed to happned as final hyphens
are stripped by slugify, but has been used in the past
and may be used in old links.
[FIX] website: update url in the footer
[FIX] orm: set default before removing magic fields

When a record is created, the magic fields (id, create_date,...) are first removed from the vals as the user should not set a value for these.
However if a value for this is given in default value (e.g. defined in an ir.value), the creation would crash (sql error : column specified more than once) as the magic column would be added again.
[FIX] product_visible_discount: multicurrency pricelists

When we compute the discount of a product to display (result of product_id_change), we compare prices in the currency of the product while we expect prices in the currency of the pricelist. opw 606188
[FIX] calendar: onchange_dates: protect against void dates (for example when creating a meeting through the form view)
[IMP] base: show possible titles for companies (opw 608243)
[FIX] account: res.partner: limit access to "total_invoiced" field to group "group_account_invoice". Use SUPERUSER_ID to access data
[FIX] Model.load(): extra error checking while importing data

If any missing or partially incorrect values cause
an exception other than a psycopg2 error, we should
still catch it, rollback that record and report
the error, rather than letting bubble and fail
without any feedback to the user.

Fixes #1485
[MERGE] Forward-port 7.0 up to 9411a2da
[FIX] website: OpenERP->Odoo in website footer
[MERGE] Forward-port saas-3 up to fc92027
[MERGE] Forward-port saas-3 up to 7273474
[FIX] product_visible_discount: no crash when no pricelist passed or product without company

Fixes an error introduced in f6fb2b6
[MERGE] Forward-port saas-5 up to 37ba23d
[MERGE] Forward-port 8.0 up to d706adb