[FIX] fetchmail: do not delete a failing email when using POP

In case of IMAP, the email is simply set as read but in case of POP, the email is deleted. To avoid loosing data (e.g. misconfiguration of server), the email is kept for POP.
Bug lp:1296724, opw 605667
[FIX] point_of_sale: generate bank statement with commerical partner

When a pos session is closed & confirmed, the account.move were generated with the commercial partner except for the bank statement which prevented automatic reconciliation.
This patch uses the commercial partner also for bank statement.
Fixes #1558, #1764