Improve profiling framework for DB transactions

[pierre]

DAO and DAO_DETAILS only record ResultSet execution time, which is good for checking slow queries but this doesn't give us the full DB picture. In particular, it doesn't measure the impact of the following calls:

• GET/SET TRANSACTION ISOLATION LEVEL
• SET AUTOCOMMIT
• EXECUTE STATEMENT
• DEALLOCATE PREPARE STATEMENT
• COMMIT

We don't have to go too low level (if needed, we can always enable the jdbc.audit logger), but it would be useful to at least measure the time taken to run full transactions.