Extension of DBDuplicateEntry exception

Added new field 'value' for DBDuplicateEntry exception.
It shows duplicated value for mysql and postresql 9.x engines
and is read from the error message using regular expressions.

The duplicated value can't be extracted from SQLite error messages,
so we do our best here for other db backends that we support.

Change-Id: I647e314cafe8ceb570bf18948d6ab83ab6afef97
Merge "Extension of DBDuplicateEntry exception"