ENH Use extension hook instead of proxy-db

[emteknetnz]

Issue #73

Requires silverstripe/silverstripe-framework#11209

To test logging, put something like this in AuditFactory::create():40

// don't merge this
$log->pushHandler(new \Monolog\Handler\StreamHandler('/var/www/out.txt'));

Then login an as an admin and create a new member - you should see a "modified Member" row added in the log

[sabina-talipova]

LGTM. Test locally. Work as expected.