Cleanup alias usage and definition. Prepare code to ease future changes and
improvements. Notably
* add a 'alias_email' computed field on the mixin allowing to have the
complete alias email when set, and False in case it is inactive or linked
to an inactive alias domain;
* remove unnecessary alias_id field definition when just the help differs
from the standard definition coming from the 'mail.alias.mixin';
* use fields coming from 'inherits' instead of using alias_id and its sub-
fields; notably use 'alias_display_name' and 'alias_email' fields;
* remove useless custom code and management;
* improve alias parameters support code in configuration parameters;
Task-3453343 (Mail: Cleanup Alias Usage)
Prepares Task-36879 (Mail: Support MultiCompany Aliases)
Part-of: odoo/odoo#130632
Thibault Delavallée
638e0f658d