Add support for database appender

[jvz]

This should offer a configuration UI and ability to output audit log events to a configurable JDBC datasource. Determine whether it would be better to offer a sort of mapping UI to the user to configure which tables and columns get mapped to what log message properties or if it would be easier to predefine a table layout using something like Liquibase.

A mechanism for choosing a JDBC driver will also need to be provided. Postgres can easily be bundled, but other drivers tend to have licensing issues to investigate.

[aarthira]

I will take up this investigation and post my results before we go for the implementation.