[IMP] account: Optional bank statements

Bank statements are now optional in accounting. The users add statements directly and can assign statements for control reasons.
The users can enter end date and end balance real for the statements and attach the bank statement scan.

The system checks if there is a gap (lines without statement) before current statement and warns the user
with decoration, also we check if the ending balance match the accumulated balance of the last line.

Bank statement lines now show an accumulated balance and can be sorted by drag and drop in the same date, if the user drags a line
to a position with lines of another date, it simply doesn't have any effect.
Rename accumulated balance to cumulative balance, a better name

closes odoo/odoo#99092

Task: 2879904
Related: odoo/upgrade#3906
Related: odoo/enterprise#30824
Signed-off-by: Laurent Smet <las@odoo.com>