Replace audit database with simple log based implementation

We've seen repeated instances over the years where the current auditing implementation has imposed significant overhead on Nexus Repo, and we've had to ask customers to disable it.  This is unfortunate, because the very customers who would want auditing the most (our largest customers) often cannot use it.

Nexus IQ Server has recently implemented auditing using a simple log file based implementation.  We've had zero complaints about this from customers so far about this simple implementation.

I propose that we eliminate the current audit database and UI, and replace it with a log based implementation.   By moving to a lightweight implementation we could even have it enabled by default, which would be tremendously helpful when trying to solve customer problems.