Monal causes excessive entries in audit log

[mwild1]

Monal is relatively unique among clients in that it reconnects to the server extremely frequently (by design). This can cause an excessive number of entries in the server's audit log under normal usage. The performance of large audit logs should be improved when #196 becomes the default configuration. However it's also a good idea to avoid these excessive entries in the first place.

For example, it should be acceptable to skip recording entries successfully using FAST auth with a recognised client ID.

Edit: Apparently Monal does not implement FAST yet, so this can't be done securely.