refactor QSqlTableModel::setRecord()

refactor QSqlTableModel::setRecord()

-Do not use setData()
We're using ModifiedRow now so it makes sense to buffer the changes
and submit the row at once. This improves readability and
encourages further haromonization of the editing strategies.

-No longer need temporary change to OnRowChange
Previously, the strategy was temporarily changed from OnFieldChange
to OnRowChange in order to obtain the desired behavior from setData().
Now, since we don't use setData(), we can program the desired behavior
here and don't need this trick.

-Comment historical idiosyncracies/bugs

Change-Id: I6d9e2a69e1571a74c630ad1392e15b60fc0ad3f2
Reviewed-by: Yunqiao Yin <charles.yin@nokia.com>