Logger improvement

[carmenfan]

As far as I understand it, boost_log_trivial is inefficient (something to do with creating a new sink every time) and we should look into using the standard boost logger.

Also, instead of using a macro to directly map repoError repoTrace etc. to BOOST_LOG_TRIVIAL, we should have our own LoggerStream that should do the same thing to decouple the relationship, This will allow programs built on top of the bouncer (i.e. gui) can use the same instance of logger without using a special function (repoLog and repoLogError atm). This is probably naturally achieved when we move onto the standard boost logger.