Adds the possibility to give formatLang() a 'rounding_mode' (any Decimal rounding mode)
and an amount_rounding ('decimals', 'units', 'thousands', 'millions' and 'lakhs').
'amount_rounding' will display the amount in the given unit. For example, 10456 in 'thousands' will be 10.
task-3626894
closes odoo/odoo#151314
Related: odoo/enterprise#55218
Signed-off-by: John Laterre (jol) <jol@odoo.com>