[IMP] account, l10n_xx: change CoA loading methods

Before, we only had a public method that installed
the CoA for the current active company.

With the multi-company changes, it was not
possible anymore to install a module with a
demo company and then have the CoA installed
in that demo company correctly.

We changed that public method to be able to
put an extra optional parameter and shortened
its name to try_loading instead of
try_loading_for_current_company.  The method that
it calls when there is no chart installed
is made private and renamed to _load.

closes odoo/odoo#35703

Signed-off-by: Quentin De Paoli (qdp) <qdp@openerp.com>