This change adds some basic logging support for Review Board. It does not handle logging of every page access, as that's the job of the web server, but instead handles timed operations such as diff generation, patching files, and loading from the repository. This should help figure out where bottlenecks are happening in the future.

Users can customize the basic logging settings (enabled, log directory and whether to allow the ?profiling=1 parameter for code profiling) through the admin UI. Any customizations cause logging to be restarted.

Verified that logging and restarting of logging works. Also tested code profiling and diff generation logging.