Send Velocity log to SLF4J (via Commons Logging)
Enable connection debugging
Enhance connection wrapping: logging, configuration, mariadb

- Log information about database and driver.
- Check for supported database/version.
- Add system property 'zanata.connection.use.wrapper' for explicit
  control.
- Disable connection wrapping for mariadb as well as mysql.
- Log what WrapperManager does.