Centralized error log storage

[adehnert]

When errors occur, an email gets sent to asa-db@ with details. This is great and has found many bugs for me. It would be awesome, however, if these were also stored in some fashion such that I can easily see a summary of, eg, what exceptions we've hit. It would also be neat if this let us easily track frequency of various warnings or informational messages.

I believe that third-party tools already exist to do this, so we should set one up. (See also #200 for the performance counterpart to this.)