[FIX] don't mess up search's id order

res_partner_category's name_search uses read, which is bad as it messes up the object's search order. This leads to weird (=the order the database returns) ordering as well in the Many2ManyTags widget's search pulldown as in tree views showing a list of categories.

This is a verbatim copy from the relevant section of https://github.com/odoo/odoo/commit/cbe2dbb672a6c55d86f2e515f9d1cdfee426ef80
(no cherrypick possible as this is a huge commit of evil), and as such, it also fixes display of multilevel categories, which doesn't seem bad to me either.

What's the policy here, there's no separate issue for this and it's already fixed in upstream - do we create another one on OCB or is this PR issue enough?