Convert our use of SQLite to use RETURNING clauses

[dkfellows]

This changes our Python code to use a RETURNING clause instead of using the lastrowid property, mirroring a change already in the Java code. It also gets rid of DsDatabaseException; plain old DatabaseException should be good enough.

Note that this requires that we are running against a new enough Python to support RETURNING clauses. I don't know if 3.8 is new enough. Works with 3.8 in test.

[Christian-B]

This looks good assuming it works.

Can we also do something similar with rowcount

May also be an idea to convert the DatabaseReader use of fetchone

[coveralls]

coverage: 42.358% (+0.07%) from 42.293% when pulling 52802b6 on returning into 0f3b084 on master.