Added a log file and view for the ER5 performance metric. The PerformanceMiddleware response handler checks whether the user tried to create an event or annotation, and records the status code of the response. The view 'performance' displays stats for performance over the last three days. NB: This solution is fragile for several different reasons. But the most egregious is that permissions on the log file cause conflicts with django management commands. This will need to be addressed in the future.