Convert to unicode the string of predefined search field

DomainParser expect to work with unicode and gettext return string encoded in
utf-8 (coding of the po file)

issue3440
review1301002
Manage exclude field on many2one

issue3173
review1211002
Add support for add_remove on many2many widget

If a one2many is displayed with the many2many widget, the widget should support
the add_remove attribute.

review1231002