[FIX] account: prevent selecting company's contacts for manual account.move.line

Only the commercial partner (parent company) should be set in partner field of
an account.move.line.
Fixes #4261, opw 618763
[FIX]stock: return of 'To Be Invoiced' picking should also be invoiced

When creating a return picking, the default invoice state is 'To Be Invoiced' if
returned picking was invoiced. However if the invoice of the picking has not
been generated yet (state '2binvoiced'), the return should also be invoiced.
Fixes #4002
[FIX] account: aged partner balance, advance partial payment

Partners totals were not correct if the partner paid partially an invoice in advance
For an invoice of 20.000 in the future, with a payment made in advance of 5000
The column not due must contains 20.000, as the amount is not yet due
One of the column 1-30, 30-60, ... (accordingly on when the payment was made). must contains -5000
The total should be 15.000
[FIX] account_check_writing: correct domains on allow_check

Fixes #4269
[FIX] #4309 Attachments with res_id=0 should not be considered orphaned
[FIX] #4309 Attachments with res_id=0 should not be considered orphaned
Merge branch '7.0' of github.com:odoo/odoo into fix_4309_non_orphaned_attachments
Merge branch 'fix_4309_non_orphaned_attachments' into 7.0