QSqlTableModel: derive primary values from database values

QSqlTableModel: derive primary values from database values

Primary values are used to map a row in the model to a row in the
database table. It is critically important between submitting a
change and the following select (which refreshes the query) to have
updated primary values. Otherwise, if the change affected the primary
values, additional changes before select will misbehave.

Change-Id: I5d08dd70ac5d3f06cd9d3186a439f4c80a037c2d
Reviewed-by: Yunqiao Yin <charles.yin@nokia.com>