[FIX] account_anglo_saxon: correctly set the accounts for returns

The generated moves on a return should be the reverse of the outgoing move.
Fixes #1817, opw 604417
[FIX] mail: chatter read more/less expand first oe_msg_body_long/short in the first oe_msg_body

Otherwise, if the mail itself contains a oe_msg_body_long (because sent in the mail history), it will open that one
[FIX] stock/purchase: dates and currency rates

Use the currency rate of the purchase date instead of the one of at the reception time (opw 610430)
[FIX] hr_timesheet_sheet: avoid error when sort attendances

When an attendance line is edited, the tuple has no key 'name' which lead to a traceback.
Fixes #546
[FIX] kanban: wrong condition to reset the dataset index

The dataset index should be reset either if the dataset is empty or the index is greater than the records size
[MERGE] forward port of branch 7.0 up to a218a9e
[MERGE] forward port of branch saas-3 up to 5bd0249