SQLite safety and security options

[felix-schwarz]

Once feature-complete, evaluate impact on performance and reliability/data safety of the following SQLite options:

• journal_mode: http://www.sqlite.org/pragma.html#pragma_journal_mode
• secure_delete: http://www.sqlite.org/pragma.html#pragma_secure_delete
• auto_vacuum: http://www.sqlite.org/pragma.html#pragma_auto_vacuum (and vacuuming in general)