[ADD] sale: validity date in sale order report
[FIX] survey: minor view fixes
[FIX] survey: remove duplicate browse record

The `prepare_result` dict shouldn't keep a browse record of a survey, as it
is explicitely passed to the template by the controller
`survey_reporting`
[DOC] survey: retroengineering

A bit of commenting in order to help future debugging and unf**king of
the survey reporting tool.
[FIX] survey: comments are properly recorded now
[FIX] survey: correct counting of finished answers