Improve Observers

[jaumef]

The current observers field is a comma-separated string:

It would be better to use a Many2Many with res_partner_address

Also would be great to have a BCC Observers as "secret observers"

[ecarreras]

To don't break the behavior, maybe we can convert the new field to the comma separated list

[jaumef]

TODO

Replace the Watchers field with a new page with "many2many" fields alongisde with their comma separated list related field. We need both lists:

• Watchers (CC)
• Secret watchers (BCC)

The many2many fields are related to a res.partner.address.
Then we may do an on_change method for those "many2many" to add the related addresses to the string field without duplicated addresses and respecting the addresses that are added manually.